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PROFESSOR: OK, it's
time to get started.

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Pay attention to the
clicker questions.

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All right, I'll give
you 10 more seconds.

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Not bad, we seem to
be in the 70's.

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All right.
 

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So if you didn't have time
to click in, let's consider

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what's going on here.
 

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What's true about the
relationship of q and k here?

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So is q less than
or greater than k?

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Less than.
 

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And so you have to think about
what that means in terms of

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where we are now in the
reaction and where the reaction

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is at equilibrium, and I like
to think about it in terms of

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products -- are there more
products now, or are there more

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products at equilibrium.
 

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So if q is less than k, then
there are more products at

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equilibrium, and so the
reaction will shift

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toward products.
 

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So it's going to move in the
direction to reach equilibrium,

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since k is a bigger number than
q, and both of these terms are

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products over reactants,
there'd mean there's more

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product at equilibrium then
there are now, and so the

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reaction is going to
shift toward products.

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All right, so we're at 73%.
 

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Let's see if by the end of
today, we can get up to 90 on

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these kinds of questions.
 

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All right, so we're going to
continue to consider external

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effects on k in today's class.
 

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I also wanted to mention that
on each of the handouts for the

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lectures, I have the
corresponding reading material

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listed on the handout, and I've
listed it as section numbers in

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the chapters rather than page
numbers, so that's a little

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bit of a difference.
 

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And the reason why I've done
that is that we've had many

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different versions of the book
in this class, and they don't

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seem to change the section
titles or the section numbers,

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but they do change the page
numbers associated with them.

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So if I give you section
numbers then you should be able

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to use of whichever version of
the book is available to you.

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So that's how I have it listed
now, and the reading assignment

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is also listed on each
problem-set as well.

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So when you're going over the
handouts later studying for the

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exam, you can see where in the
book this particular lecture,

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the material is, so you can
go and do that reading.

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All right, so we talked at the
end of the class last time

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about the Le Chatelier's
principle, and this is a

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principle that you can use to
predict the direction of change

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of a reaction -- whether it'll
shift to the right or

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shift to the left.
 

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And simply stated, that systems
tend to respond in such a

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way to minimize the stress.
 

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So if something is added to the
reaction, the reaction will

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shift in a way to minimize that
stress caused by the thing

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that's added to the system.
 

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So, we talked about adding
reagents and removing products

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last time, and now we're going
to go on and talk about

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what happens when you
change the volume.

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So if you have a system at
equilibrium and you change the

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volume of it, and here in
particular we're talking about

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a gaseous system, what's
going to happen?

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So what do we know about
volumes when it comes to gases?

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We say that a decrease in
volume of the gaseous

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system causes an increase
in total pressure.

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What equation leaps to your
mind when I say those words?

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Exactly, p v equals n r t.
 

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Yes.
 

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So there's a relationship
between pressure and volume --

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n is the number of moles, r is
our gas constant, and

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t is our temperature.
 

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This is one of the things that
usually sticks from high

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school, and if you haven't seen
it before, it's pretty easy to

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get up to speed with
this equation.

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So Le Chatelier's principle
then predicts that the system

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will respond if possible in a
way to reduce the

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total pressure.
 

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So if you decrease the volume
and you cause an increase in

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total pressure, Le Chatelier
says wait a minute, the system

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wants to respond to minimize
that stress, so that it's going

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to respond in such a way to
reduce that total pressure.

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So let's look at some
examples of this.

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So we have an example of a
reaction where we have two

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moles of p 2 gas going to
one mole going to p 4 gas.

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And I have a little cartoon
here to show this.

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So we have our p 4 gas up
here, and our p 2 gas.

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All right, so what's going to
happen if we're going to change

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the volume of this system?
 

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So if we're going to decrease
the volume of the system,

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then the reaction should
shift toward products.

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So let's think about that.
 

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So here in the middle we have
our sort of system, and then on

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one side what happens when you
decrease the volume and

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on the other side we're
expanding the volume.

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So first, let's consider our
system when we're going to

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compress that volume,
decrease that volume.

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So what would be true is that
the system's going to respond

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in such a way to minimize that
stress that has been put

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forward by decreasing the
volume, and you're going to try

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to compensate for that, and in
this case you can compensate by

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a shift toward products.
 

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Why is that?
 

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Well, it all has to do
with the stoichiometry of

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this equation up here.
 

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So for every two moles
of reactants, you get

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one mole of products.
 

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So if you shift from the two to
the one, that will cause a

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decrease in pressure, and so
that will help compensate for

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the increase in pressure caused
by the switch in volume.

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So you're going to respond
in such a way to compensate

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for that stress.
 

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So a shift to the reaction
to the right decreases

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the total pressure.
 

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So now let's think more
about why this is true.

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Let's think about it from a
math perspective and also just

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this qualitative perspective.
 

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So let's consider it
in terms of q and k.

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So suppose our volume is
decreased by a factor of 2,

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let's just make it easy, and we
have constant temperature here.

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So this change will increase
the partial pressure of both

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gases, the reacting gas and the
product gas, and it's going

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to increase them both by the
same amount, by 2 initially.

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So let's look at our equation
for q, the reaction quotient.

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We have partial pressure of
products over the partial

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pressures of the reactants,
a raise to the coefficient

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00:08:16 --> 00:08:17
to the equation.
 

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So initially you're going to
increase the pressure, partial

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pressure of both gases by 2 --
then your product by 2, the

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reactant by 2 -- but
here it's 2 squared.

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So overall, q becomes 1/2.
 

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So q decreases by a
factor of 2, and so q

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becomes less then k.
 

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And so, in the clicker
question, we talked about what

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happens when q becomes less
than k, and what happens there

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is you're going to shift toward
products until q

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equals k again.
 

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So you can think about this in
terms of q and k, and you can

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also just think about it how
many moles of gas are on one

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side, how many mold of gas on
the other side, and how are you

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going to correspond, how are
you going to decrease or

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minimize the stress
on the system.

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00:09:08 --> 00:09:14
All right, so let's think about
what happens if we increase the

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volume, so here is our system
and now we're going

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to expand it.
 

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If we're going to increase the
volume, what's going to happen

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to the total pressure?
 

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I'm hearing it, but I
want everyone to answer.

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Thank you.
 

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All right, so it will
decrease the pressure.

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And what that's going to do is
shift toward reactants, because

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we want to compensate for that
decrease in pressure, and to do

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that, we can increase the
pressure by switching or

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00:09:50 --> 00:09:53
shifting the reaction
toward the reactants.

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So again, we're going from one
mole of product on one side

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to two of the reactants.
 

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So here, we see a shift
toward the reactants.

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And so, this shift to the left
is going to increase the total

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pressure to compensate for the
decrease in pressure that was a

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result of this applied
force to the system.

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And we could do this again
in terms of q and k.

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Now we're going to get
a little trickier.

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What happens if we add an inert
gas to a system increasing

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00:10:39 --> 00:10:44
the total pressure at
constant temperature?

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So we're not adding one of the
reactants or one of the

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products, we're adding an inert
gas, and we're increasing

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00:10:49 --> 00:10:51
the total pressure.
 

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What's going to happen?
 

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There's a couple of options,
what do you think?

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00:11:05 --> 00:11:09
How about nothing.
 

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Why would nothing happen?
 

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00:11:13 --> 00:11:17
Well, q depends on the partial
pressure of the reactant

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gas and the product gas.
 

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And in this particular example,
the partial pressures

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are not changing.
 

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We are changing the total
pressure of the system

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by adding an inert gas,
but we're not changing

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00:11:30 --> 00:11:33
the partial pressure.
 

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So let's take this opportunity
to review partial pressures, or

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if you haven't seen it before,
I'm going to tell you

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everything you need to know
about partial pressures.

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So here's a little review, or
for the first time, description

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00:11:49 --> 00:11:51
of partial pressure.
 

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So what is the definition?
 

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The partial pressure is the
pressure that each gas would

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exert if it were present
alone in the container.

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So in this example, we have
oxygen in a container, and

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we have one atmosphere
of pressure.

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00:12:09 --> 00:12:12
In the second one there's
nitrogen in the container with

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00:12:12 --> 00:12:15
one atomosphere of pressure.
 

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00:12:15 --> 00:12:18
If you put this amount of
oxygen and this amount of

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nitrogen together in a
container, then you would have

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00:12:22 --> 00:12:26
two atmospheres of total
pressure, but you're still

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going to have one atmosphere of
partial pressure for oxygen,

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00:12:31 --> 00:12:35
and one atmosphere of partial
pressure for nitrogen.

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So it's as if the gas is
alone in the container.

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That's the definition
of partial pressure.

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00:12:43 --> 00:12:48
So let's look at
some equations.

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00:12:48 --> 00:12:52
So the partial pressure of a
gas, p to sub a, is equal to

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00:12:52 --> 00:12:57
the number of moles of that
gas, and we also have in this

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00:12:57 --> 00:13:00
equation, r, our gas constant,
t, our temperature,

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00:13:00 --> 00:13:02
and v, our volume.
 

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00:13:02 --> 00:13:05
The total pressure on the
system, which is what this two

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00:13:05 --> 00:13:10
atmospheres is, is equal to the
partial pressure of gas a,

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00:13:10 --> 00:13:13
which would be the partial
pressure of the oxygen at one

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00:13:13 --> 00:13:16
atmosphere, the partial
pressure of the nitrogen at one

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00:13:16 --> 00:13:18
atmosphere, that's
all we have here.

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00:13:18 --> 00:13:21
So the partial pressure of
those two, of one plus one,

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00:13:21 --> 00:13:24
we have two for a total.
 

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00:13:24 --> 00:13:29
And that's equal to the
total number of the moles.

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00:13:29 --> 00:13:32
So in these problems, we're
going to be considering partial

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00:13:32 --> 00:13:34
pressure, and the question
you're going to be asking

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00:13:34 --> 00:13:37
yourself in all of these
different wordings of the

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00:13:37 --> 00:13:41
question is is the partial
pressure of the gas changing?

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00:13:41 --> 00:13:43
That's a very important
question to ask because

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00:13:43 --> 00:13:50
that'll help you answer
the questions correctly.

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00:13:50 --> 00:13:54
So let's go back to the
original question, what happens

223
00:13:54 --> 00:13:59
if an inert gas is added to the
container, increasing the total

224
00:13:59 --> 00:14:02
pressure at constant
temperature?

225
00:14:02 --> 00:14:07
And the answer is nothing,
because q is not affected,

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00:14:07 --> 00:14:10
because q depends on the
partial pressures, and the

227
00:14:10 --> 00:14:12
partial pressure
isn't changing.

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00:14:12 --> 00:14:15
We aren't changing the number
of moles of the gas in

229
00:14:15 --> 00:14:20
question, we're just changing
the total pressure of the

230
00:14:20 --> 00:14:22
system, we're adding
an inert gas.

231
00:14:22 --> 00:14:25
And because partial pressures
don't change, q doesn't change,

232
00:14:25 --> 00:14:27
and if q doesn't change,
there's no response

233
00:14:27 --> 00:14:30
from the system.
 

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00:14:30 --> 00:14:34
So a lot of the questions in
this unit, they're not actually

235
00:14:34 --> 00:14:37
very difficult, but the
wording can be tricky.

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00:14:37 --> 00:14:40
And so when you're doing these
problems, you have to be

237
00:14:40 --> 00:14:45
thinking about what is changing
and what isn't changing to

238
00:14:45 --> 00:14:47
be able to get these
questions correct.

239
00:14:47 --> 00:14:50
And if you do that, then these
are some nice questions for you

240
00:14:50 --> 00:14:54
to get right on the exams --
they're short, they're good

241
00:14:54 --> 00:14:59
questions to go after.
 

242
00:14:59 --> 00:15:00
All right.
 

243
00:15:00 --> 00:15:03
Let's see how you're
doing with this.

244
00:15:03 --> 00:15:07
What happens if an inert gas is
added to the container, but the

245
00:15:07 --> 00:15:11
total pressure is now kept
constant, temperature

246
00:15:11 --> 00:15:14
is also constant.
 

247
00:15:14 --> 00:15:15
So let's think about this.
 

248
00:15:15 --> 00:15:57
OK, let's take 10 more seconds.
 

249
00:15:57 --> 00:16:01
OK, we're going down into the
60's -- again, we're heading

250
00:16:01 --> 00:16:04
toward the 90's by the end,
but this is actually new

251
00:16:04 --> 00:16:07
material, so that's fine.
 

252
00:16:07 --> 00:16:09
All right, so let's
think about it.

253
00:16:09 --> 00:16:13
So the reaction's going to
shift toward reactants.

254
00:16:13 --> 00:16:15
Let's think about why,
let's break it down.

255
00:16:15 --> 00:16:19
And what was important is that
hint that for the pressure to

256
00:16:19 --> 00:16:22
be kept constant, the volume of
the container must

257
00:16:22 --> 00:16:23
have increased.
 

258
00:16:23 --> 00:16:27
So let's take a look at that.
 

259
00:16:27 --> 00:16:31
So if the total pressure was
kept constant, if the total

260
00:16:31 --> 00:16:35
pressure didn't change when
you added an inert gas, the

261
00:16:35 --> 00:16:37
volume must have changed.
 

262
00:16:37 --> 00:16:38
Let's look at this.
 

263
00:16:38 --> 00:16:41
Say oxygen is our gas
of interest, and n

264
00:16:41 --> 00:16:43
2 is an inert gas.
 

265
00:16:43 --> 00:16:47
If we added an inert gas
to our system, the total

266
00:16:47 --> 00:16:48
pressure should go up.
 

267
00:16:48 --> 00:16:52
If it doesn't, then something
else must have changed, and

268
00:16:52 --> 00:16:55
what must have changed
is the volume.

269
00:16:55 --> 00:17:01
Otherwise the total pressure
would not have stayed the same.

270
00:17:01 --> 00:17:05
So the volume of the container
must have increased if

271
00:17:05 --> 00:17:09
the pressure is the same.
 

272
00:17:09 --> 00:17:16
So then we asked the question,
if you increase the volume,

273
00:17:16 --> 00:17:19
what happens to the reaction,
how does it shift?

274
00:17:19 --> 00:17:25
If you increase the volume, if
you expand the volume, then

275
00:17:25 --> 00:17:29
you're going to shift from, in
this case where you have one

276
00:17:29 --> 00:17:34
mole to two moles toward
reactants, you will, as the

277
00:17:34 --> 00:17:38
volume increases, then you're
going to have a change in the

278
00:17:38 --> 00:17:41
partial pressure of the gas --
all of a sudden the gas has a

279
00:17:41 --> 00:17:46
lot more room, and its pressure
is going to decrease, the

280
00:17:46 --> 00:17:48
partial pressure will decrease.
 

281
00:17:48 --> 00:17:51
It has a lot more space for
itself -- it's like it's

282
00:17:51 --> 00:17:53
in there all by itself.
 

283
00:17:53 --> 00:17:56
Partial pressure, you can think
of it as selfish gas molecules,

284
00:17:56 --> 00:17:57
they don't care what
else is there.

285
00:17:57 --> 00:18:00
They're only thinking
about how they're fairing

286
00:18:00 --> 00:18:02
in this environment.
 

287
00:18:02 --> 00:18:06
So then we want to shift in a
way that compensates for that

288
00:18:06 --> 00:18:08
stress that increases the
pressure, so we move from one

289
00:18:08 --> 00:18:12
molecule to two molecules.
 

290
00:18:12 --> 00:18:17
So it's all about the
partial pressure q and k.

291
00:18:17 --> 00:18:19
So again in these questions
you have to dissect

292
00:18:19 --> 00:18:20
what's going on.
 

293
00:18:20 --> 00:18:22
What has changed?
 

294
00:18:22 --> 00:18:25
The questions are often phrased
in such a way, something's kept

295
00:18:25 --> 00:18:28
constant, but if something's
kept constant, you have to ask

296
00:18:28 --> 00:18:31
the question, to keep it
constant, did something have to

297
00:18:31 --> 00:18:33
change for that to be true.
 

298
00:18:33 --> 00:18:35
So again, the wordings
of these can be tricky.

299
00:18:35 --> 00:18:36
Do you have a question?
 

300
00:18:36 --> 00:18:39
STUDENT: [INAUDIBLE]
 

301
00:18:39 --> 00:18:47
PROFESSOR: So, the question
is is it necessary for it to

302
00:18:47 --> 00:18:48
try to increase pressure.
 

303
00:18:48 --> 00:18:50
This is just the predictive
tool of Le Chatelier.

304
00:18:50 --> 00:18:54
Le Chatelier would predict that
if the system has changed in

305
00:18:54 --> 00:18:56
such a way, such as volume
increases so the partial

306
00:18:56 --> 00:18:59
pressure decreases, that the
system will shift in a way

307
00:18:59 --> 00:19:01
to minimize that stress.
 

308
00:19:01 --> 00:19:05
And to minimize that stress,
you would increase the partial

309
00:19:05 --> 00:19:07
pressure by doing the shift
from one mole to two.

310
00:19:07 --> 00:19:12
So again, this is Le
Chatelier's predictive, how you

311
00:19:12 --> 00:19:15
would predict the direction of
the shift based on the simple

312
00:19:15 --> 00:19:18
idea that a system where a
stress is applied, the system

313
00:19:18 --> 00:19:22
will respond in a way to
minimize the stress.

314
00:19:22 --> 00:19:26
And again, I talked about last
time that this concept of

315
00:19:26 --> 00:19:30
minimizing stress is difficult
for some MIT students, but you

316
00:19:30 --> 00:19:33
just sort of have to memorize
that in this case we're

317
00:19:33 --> 00:19:43
predicting how a system will
shift to minimize that stress.

318
00:19:43 --> 00:19:45
OK.
 

319
00:19:45 --> 00:19:48
So if you need a review of
partial pressure, go over this.

320
00:19:48 --> 00:19:51
This part, it looks a little
challenging at first, and some

321
00:19:51 --> 00:19:54
of the questions you really
have to sit down and dissect

322
00:19:54 --> 00:19:57
what's going on, and for most
people, once they get there,

323
00:19:57 --> 00:20:00
that part, those are good
questions, you look forward

324
00:20:00 --> 00:20:04
to them on the exam.
 

325
00:20:04 --> 00:20:07
So now, we've talked about
adding reagents, we've talked

326
00:20:07 --> 00:20:11
about removing reagents,
removing products, adding

327
00:20:11 --> 00:20:17
products, shifts in volume, and
now we're going to talk about

328
00:20:17 --> 00:20:20
changing the temperature.
 

329
00:20:20 --> 00:20:23
So here, Le Chatelier's
principle, it's a little

330
00:20:23 --> 00:20:28
bit more fuzzy, but it
still basically works.

331
00:20:28 --> 00:20:32
So if you talk about raising
the temperature of a mixture

332
00:20:32 --> 00:20:37
at equilibrium, then Le
Chatelier's principle would

333
00:20:37 --> 00:20:41
suggest that the system is
going to respond in such a

334
00:20:41 --> 00:20:42
way to minimize that stress.
 

335
00:20:42 --> 00:20:47
So if you're adding heat, the
system wants to respond in a

336
00:20:47 --> 00:20:50
way to absorb some of the
heat, to counterbalance

337
00:20:50 --> 00:20:54
that change to the system.
 

338
00:20:54 --> 00:20:57
So let's take a look at this.
 

339
00:20:57 --> 00:21:01
So let's think about raising
the temperature of an

340
00:21:01 --> 00:21:07
exothermic reaction.
 

341
00:21:07 --> 00:21:09
So what's going to happen here?
 

342
00:21:09 --> 00:21:14
Raising the temperature of an
exothermic reaction, favors the

343
00:21:14 --> 00:21:18
formation of reactants, would
shift toward reactants.

344
00:21:18 --> 00:21:20
Well, why would this be true.
 

345
00:21:20 --> 00:21:24
Well, you can think about this
very simplistically that in an

346
00:21:24 --> 00:21:29
exothermic reaction, you're
going to be producing heat in

347
00:21:29 --> 00:21:33
the forward direction and
absorbing heat in the

348
00:21:33 --> 00:21:35
reverse direction.
 

349
00:21:35 --> 00:21:38
So if it's an exothermic
reaction, that means it's

350
00:21:38 --> 00:21:41
exothermic in the forward
direction, which would mean

351
00:21:41 --> 00:21:45
it was endothermic in
the reverse direction.

352
00:21:45 --> 00:21:49
So if you raise the temperature
of an exothermic reaction,

353
00:21:49 --> 00:21:53
you're adding heat, the system
wants to respond in such a way

354
00:21:53 --> 00:21:58
to absorb that heat, so it
would shift toward the

355
00:21:58 --> 00:22:02
endothermic direction of the
reaction, which is the reverse

356
00:22:02 --> 00:22:05
direction toward reactants.
 

357
00:22:05 --> 00:22:09
So add heat, system wants
to shift to absorb

358
00:22:09 --> 00:22:10
some of that heat.
 

359
00:22:10 --> 00:22:13
So in this part you think about
the direction of the reaction,

360
00:22:13 --> 00:22:16
whether it's exothermic or
endothermic, and then think

361
00:22:16 --> 00:22:19
about compensating
for that stress.

362
00:22:19 --> 00:22:25
Endothermic reaction, again,
they say it's an endothermic

363
00:22:25 --> 00:22:27
reaction, it means it's
endothermic in the

364
00:22:27 --> 00:22:29
forward direction.
 

365
00:22:29 --> 00:22:32
So heat is being absorbed in
the forward direction -- again

366
00:22:32 --> 00:22:35
this is just sort of a very
simplistic way to

367
00:22:35 --> 00:22:37
think about it.
 

368
00:22:37 --> 00:22:41
So if you raise the temperature
then, you want to absorb that

369
00:22:41 --> 00:22:44
heat, according to Le
Chatelier's principle, and

370
00:22:44 --> 00:22:51
so that would favor a
shift toward products.

371
00:22:51 --> 00:22:56
So let's look some
more at this.

372
00:22:56 --> 00:23:01
The predictive tool
here is delta h.

373
00:23:01 --> 00:23:04
So delta h, whether the
reaction is exothermic or

374
00:23:04 --> 00:23:08
endothermic, is going to be a
predictive tool in thinking

375
00:23:08 --> 00:23:13
about the direction of change,
when heat is added to a system

376
00:23:13 --> 00:23:21
or heat is removed
from a system.

377
00:23:21 --> 00:23:24
So let's try this out.
 

378
00:23:24 --> 00:23:27
Heat is added to a system.
 

379
00:23:27 --> 00:23:30
You're given information about
your predictive tool, delta h.

380
00:23:30 --> 00:23:49
Which direction will
the reaction go?

381
00:23:49 --> 00:24:06
All right, 10 seconds.
 

382
00:24:06 --> 00:24:42
Why don't you discuss with
your friends and vote again.

383
00:24:42 --> 00:24:55
All right, 10 more seconds.
 

384
00:24:55 --> 00:24:58
Yes!
 

385
00:24:58 --> 00:25:02
I knew we could get
into the 90's.

386
00:25:02 --> 00:25:05
All right, so what type
of reaction is this,

387
00:25:05 --> 00:25:07
endo or exothermic?
 

388
00:25:07 --> 00:25:08
Exothermic.
 

389
00:25:08 --> 00:25:13
And so we're adding heat to an
exothermic reaction, so it

390
00:25:13 --> 00:25:17
wants to shift to absorb that
heat, so it wants to go in

391
00:25:17 --> 00:25:20
endothermic direction, which is
the reverse direction or

392
00:25:20 --> 00:25:24
toward the reactants.
 

393
00:25:24 --> 00:25:26
And that's how it's supposed
to work too, more people

394
00:25:26 --> 00:25:30
get the right answer after
the group discusses.

395
00:25:30 --> 00:25:34
All right.
 

396
00:25:34 --> 00:25:39
So we've been talking about the
equilibrium constant so far in

397
00:25:39 --> 00:25:43
terms of it being a constant,
it's called the equilibrium

398
00:25:43 --> 00:25:46
constant, but it's only
constant at a given

399
00:25:46 --> 00:25:47
temperature.
 

400
00:25:47 --> 00:25:53
So the equilibrium constant
changes with temperature.

401
00:25:53 --> 00:25:56
It's also true that rates
of reaction change

402
00:25:56 --> 00:25:58
with temperature.
 

403
00:25:58 --> 00:26:01
And kinetics is our last unit
in this course, and we'll be

404
00:26:01 --> 00:26:04
discussing that quite a bit.
 

405
00:26:04 --> 00:26:08
So how does the equilibrium
constant change

406
00:26:08 --> 00:26:09
with temperature?
 

407
00:26:09 --> 00:26:12
Let's consider that.
 

408
00:26:12 --> 00:26:15
So let's look at some of the
equations that we know that

409
00:26:15 --> 00:26:19
have delta h in them -- delta
h, again, is our predictive

410
00:26:19 --> 00:26:23
factor when we're talking
about changes in temperature.

411
00:26:23 --> 00:26:28
We know that delta g nought is
minus r t natural log of k, so

412
00:26:28 --> 00:26:31
the relationship with our
standard free energy, our gas

413
00:26:31 --> 00:26:35
constant temperature, and
our equilibrium constant.

414
00:26:35 --> 00:26:38
We also know that delta g
nought equals delta h nought

415
00:26:38 --> 00:26:40
minus t delta s nought.
 

416
00:26:40 --> 00:26:44
If those equations don't look
familiar, then you should go

417
00:26:44 --> 00:26:48
back and review the material on
thermodynamics because you're

418
00:26:48 --> 00:26:51
going to need it in this unit,
the next unit, the unit after

419
00:26:51 --> 00:26:54
that, and then the next two
units, and they we're

420
00:26:54 --> 00:26:55
done with the class.
 

421
00:26:55 --> 00:26:59
All right, so good to get
familiar with this now.

422
00:26:59 --> 00:27:04
All right, so we can rearrange
these in terms of solving for

423
00:27:04 --> 00:27:07
our equilibrium constant.
 

424
00:27:07 --> 00:27:10
And so we see the natural log
of the equilibrium constant

425
00:27:10 --> 00:27:15
minus delta h nought over r t,
plus delta s nought over r.

426
00:27:15 --> 00:27:19
And so, it's reasonable to
assume that for the things

427
00:27:19 --> 00:27:24
we're talking about, that delta
h nought and delta s nought are

428
00:27:24 --> 00:27:26
pretty much independent
of temperatures.

429
00:27:26 --> 00:27:29
That would be true for pretty
much any temperature we

430
00:27:29 --> 00:27:30
would be talking about.
 

431
00:27:30 --> 00:27:36
So that means that k, or the
natural log of k, is going to

432
00:27:36 --> 00:27:38
change depending on
the temperature.

433
00:27:38 --> 00:27:41
It won't change -- these other
ones are constant at all the

434
00:27:41 --> 00:27:44
temperatures, so there's a
relationship between

435
00:27:44 --> 00:27:50
equilibrium constant
and temperature.

436
00:27:50 --> 00:27:54
So you can consider an
equilibrium constant at one

437
00:27:54 --> 00:27:57
temperature, and an equilibrium
constant at another

438
00:27:57 --> 00:27:58
temperature.
 

439
00:27:58 --> 00:28:03
So we can talk about the
natural log of a k 2, of an

440
00:28:03 --> 00:28:07
equilibrium constant 2, equal
to minus delta h over r

441
00:28:07 --> 00:28:12
t temperature 2, plus
delta s nought over r.

442
00:28:12 --> 00:28:17
We can do the same thing for
another temperature, another

443
00:28:17 --> 00:28:23
temperature 1, equilibrium 1,
and if we subtract these two,

444
00:28:23 --> 00:28:26
delta s is going to cancel out,
and we're going to get this

445
00:28:26 --> 00:28:30
equation, which you know is
important because it has a

446
00:28:30 --> 00:28:34
name, so this is the
van't Hoff equation.

447
00:28:34 --> 00:28:37
And at some point later in the
course, I'll be asking you to

448
00:28:37 --> 00:28:40
come up with this name, so I
always get very excited when

449
00:28:40 --> 00:28:43
people can tell me it's a van't
Hoff equation later on, not

450
00:28:43 --> 00:28:46
that that's on a test,
but there are very few

451
00:28:46 --> 00:28:48
equations that have names.
 

452
00:28:48 --> 00:28:50
So here we go.
 

453
00:28:50 --> 00:28:51
So what does this do?
 

454
00:28:51 --> 00:28:54
Well, we can talk about the
natural log of one equilibrium

455
00:28:54 --> 00:28:58
constant over another, an
equilibrium constant k 2, which

456
00:28:58 --> 00:29:01
is the equilibrium at
temperature 2, equilibrium

457
00:29:01 --> 00:29:03
constant k 1, which is the
equilibrium constant at

458
00:29:03 --> 00:29:08
temperature 1, is going to be
equal to minus delta h nought

459
00:29:08 --> 00:29:11
over r, and then it depends
on the temperature.

460
00:29:11 --> 00:29:14
So you bracket 1 over
temperature 2 minus 1

461
00:29:14 --> 00:29:15
over temperature 1.
 

462
00:29:15 --> 00:29:19
And this just comes from
subtracting those 2 equations.

463
00:29:19 --> 00:29:23
So again, you can think about
how the equilibrium constant's

464
00:29:23 --> 00:29:26
going to change with
temperature -- that's what

465
00:29:26 --> 00:29:30
this equation does for you.
 

466
00:29:30 --> 00:29:34
So let's look at some of the
things that fall out of

467
00:29:34 --> 00:29:39
this particular equation.
 

468
00:29:39 --> 00:29:43
Let's think first about a case
where this delta h nought

469
00:29:43 --> 00:29:45
is less than zero.
 

470
00:29:45 --> 00:29:49
What type of reaction is that?
 

471
00:29:49 --> 00:29:50
Exothermic.
 

472
00:29:50 --> 00:29:54
All right, so now let's
consider a case for this

473
00:29:54 --> 00:29:59
exothermic reaction where we're
going to increase the

474
00:29:59 --> 00:30:04
temperature, and so that means
that t 2 will be greater than t

475
00:30:04 --> 00:30:08
1 -- we've increased
the temperature.

476
00:30:08 --> 00:30:12
So now let's think about what
sign the natural log of k

477
00:30:12 --> 00:30:19
2 over k 1 will have if
these things are true.

478
00:30:19 --> 00:30:21
So there's a minus in
the equation, let's put

479
00:30:21 --> 00:30:23
the minus down here.
 

480
00:30:23 --> 00:30:27
Delta h nought is negative,
it's exothermic reaction, so

481
00:30:27 --> 00:30:29
that's another negative sign.
 

482
00:30:29 --> 00:30:33
And if we're increasing the
temperature, and t 2 is greater

483
00:30:33 --> 00:30:37
than t 1, then this temperature
term will also have

484
00:30:37 --> 00:30:39
and negative sign.
 

485
00:30:39 --> 00:30:42
So if you have negative times
negative times negative, you're

486
00:30:42 --> 00:30:47
going to get a negative for
your net result over here.

487
00:30:47 --> 00:30:52
And what that will mean in
terms of k 2 and k 1, is that

488
00:30:52 --> 00:30:57
k 1 will be greater than k 2.
 

489
00:30:57 --> 00:31:00
So you can think about this
mathematically by running

490
00:31:00 --> 00:31:02
through this argument.
 

491
00:31:02 --> 00:31:06
You can also sort of think
about it in terms of what you

492
00:31:06 --> 00:31:12
would expect if you increase
the temperature in terms of

493
00:31:12 --> 00:31:15
what's the relative ratio of
products to reactants

494
00:31:15 --> 00:31:20
at equilibrium for an
exothermic reaction.

495
00:31:20 --> 00:31:24
So if you're increasing the
temperature of an exothermic

496
00:31:24 --> 00:31:29
reaction, the reaction would
want to shift in the direction

497
00:31:29 --> 00:31:33
to absorb that heat in the
endothermic direction.

498
00:31:33 --> 00:31:38
So you would expect that the
equilibrium constant that was

499
00:31:38 --> 00:31:41
at the lower temperature would
be larger than the higher

500
00:31:41 --> 00:31:44
temperature one, that there'd
be less products at this

501
00:31:44 --> 00:31:47
new higher temperature.
 

502
00:31:47 --> 00:31:50
So again, you can think about
it in terms of Le Chatelier's

503
00:31:50 --> 00:31:53
principle, or you can run
through with this equation and

504
00:31:53 --> 00:32:02
do the math and think about the
relative size of k 1 and k 2.

505
00:32:02 --> 00:32:04
So now let's think about what
happens when you decrease the

506
00:32:04 --> 00:32:09
temperature where t
2 is less than t 1.

507
00:32:09 --> 00:32:14
So we can do the same thing, we
have a negative sign here, we

508
00:32:14 --> 00:32:16
also have a negative sign
for delta h, it's an

509
00:32:16 --> 00:32:18
exothermic reaction.
 

510
00:32:18 --> 00:32:22
But now we have a positive sign
for this temperature term.

511
00:32:22 --> 00:32:25
So overall we're going to have
a positive sign for the natural

512
00:32:25 --> 00:32:30
log of k 2 over k 1, which
mathematically is going to mean

513
00:32:30 --> 00:32:35
that k 1 is less than k 2 or
that you would expect more

514
00:32:35 --> 00:32:41
products in the equilibrium
constant at higher temperature.

515
00:32:41 --> 00:32:49
All right, so that's an
exothermic reaction.

516
00:32:49 --> 00:32:52
So if you're ever having
problems with Le Chatelier, you

517
00:32:52 --> 00:32:55
can go and use the van't Hoff
equation to think about what

518
00:32:55 --> 00:32:58
you would expect in terms of
this shift, what you would

519
00:32:58 --> 00:33:01
expect if you change the
temperature of an exothermic

520
00:33:01 --> 00:33:05
reaction in terms of the
magnitude of the new

521
00:33:05 --> 00:33:06
equilibrium constants.
 

522
00:33:06 --> 00:33:12
All right, now you can do
the same for me in terms

523
00:33:12 --> 00:33:18
of this delta h nought
is greater than zero.

524
00:33:18 --> 00:33:22
Which of the following are
going to be true, and notice

525
00:33:22 --> 00:33:27
there's a possibility that all
of them are true or that just

526
00:33:27 --> 00:33:30
some of them are true or
that one of them is true.

527
00:33:30 --> 00:34:46
All right, take
10 more seconds.

528
00:34:46 --> 00:34:49
See, actually people did very
well, because e is also true,

529
00:34:49 --> 00:34:53
all of those are true,
but d was also true.

530
00:34:53 --> 00:34:58
So if we add the 30 and the
58 together, I'm very happy.

531
00:34:58 --> 00:35:03
All right, so let's look at
this -- we'll keep the

532
00:35:03 --> 00:35:06
questions up and let's consider
all of them in order.

533
00:35:06 --> 00:35:12
So the first one is that the
reaction was endothermic,

534
00:35:12 --> 00:35:16
I think everybody saw
that as being correct.

535
00:35:16 --> 00:35:19
OK, the second one talked about
the equilibrium constant is

536
00:35:19 --> 00:35:21
higher at higher temperatures.
 

537
00:35:21 --> 00:35:22
So let's look at the first one.
 

538
00:35:22 --> 00:35:27
We increased the temperature
here, and we see that if you

539
00:35:27 --> 00:35:31
work out the math or just think
about it, k 2 is larger than k

540
00:35:31 --> 00:35:35
1, so the second equilibrium
constant is greater than the

541
00:35:35 --> 00:35:39
first when you increase
the temperature.

542
00:35:39 --> 00:35:42
So that would favor then, in
an endothermic direction, if

543
00:35:42 --> 00:35:44
you're increasing the
temperature, it favors the

544
00:35:44 --> 00:35:47
endothermic direction of the
reaction, so you could think

545
00:35:47 --> 00:35:52
about the ratio having more
products at that new

546
00:35:52 --> 00:35:55
equilibrium constant at
that higher temperature.

547
00:35:55 --> 00:35:57
So that one was also true.
 

548
00:35:57 --> 00:36:00
Then let's think about when you
decrease the temperature, when

549
00:36:00 --> 00:36:05
temperature 1 is greater
than temperature 2.

550
00:36:05 --> 00:36:09
And so this would favor, then,
the exothermic direction.

551
00:36:09 --> 00:36:14
So you would expect
less products at this

552
00:36:14 --> 00:36:16
newer temperature.
 

553
00:36:16 --> 00:36:20
So, this part asked about k
1 versus k 2, and we see

554
00:36:20 --> 00:36:22
k 1 is greater than k 2.
 

555
00:36:22 --> 00:36:26
And then d says there's fewer
products and equilibrium when

556
00:36:26 --> 00:36:30
the temperature is decreased,
and that's just the word way

557
00:36:30 --> 00:36:33
of saying the same thing.
 

558
00:36:33 --> 00:36:36
So all of those are true.
 

559
00:36:36 --> 00:36:42
But again, people did very,
very well with this question.

560
00:36:42 --> 00:36:45
All right.
 

561
00:36:45 --> 00:36:50
So now we're going to combine
what we learned on Friday with

562
00:36:50 --> 00:36:55
what we learned today, and
think about ways that

563
00:36:55 --> 00:36:57
that can be applied.
 

564
00:36:57 --> 00:37:01
So why should you care about
Le Chatelier's principle?

565
00:37:01 --> 00:37:04
Well, for two reasons -- one I
think Le Chatelier had sort of

566
00:37:04 --> 00:37:08
a good life plan that when
stress is applied to the

567
00:37:08 --> 00:37:12
system, one should respond in a
way to minimize that stress.

568
00:37:12 --> 00:37:15
I think that is an
important life lesson.

569
00:37:15 --> 00:37:19
But also, it's very useful
in terms of thinking

570
00:37:19 --> 00:37:22
about maximizing a
yield of a reaction.

571
00:37:22 --> 00:37:26
So if you were going to create
an industrial process and make

572
00:37:26 --> 00:37:31
lots of money and give some of
it back to MIT to improve

573
00:37:31 --> 00:37:36
things in terms of teaching
chemistry at MIT, then you

574
00:37:36 --> 00:37:39
would want to think about these
principles, because you would

575
00:37:39 --> 00:37:40
want to maximize your yield.
 

576
00:37:40 --> 00:37:42
If you're going to be making a
product, you want to make a lot

577
00:37:42 --> 00:37:45
of that product, and so you
want to be thinking

578
00:37:45 --> 00:37:47
about these things.
 

579
00:37:47 --> 00:37:51
So we've talked about the
reaction with nitrogen

580
00:37:51 --> 00:37:54
and hydrogen making
ammonia last time.

581
00:37:54 --> 00:37:58
And this is an
exothermic reaction.

582
00:37:58 --> 00:38:03
So, there are a lot of people
who want to make ammonia --

583
00:38:03 --> 00:38:06
it's for fertilizer, and as
some of you have heard in terms

584
00:38:06 --> 00:38:11
of terrorism, it also can be
used as an explosive, so there

585
00:38:11 --> 00:38:16
are a lot of people who want
to make a lot of this.

586
00:38:16 --> 00:38:19
So how do you
maximize this yield?

587
00:38:19 --> 00:38:22
It's an exothermic reaction.
 

588
00:38:22 --> 00:38:25
So you can think
about temperature.

589
00:38:25 --> 00:38:32
So here, low temperature would
favor product, which is good.

590
00:38:32 --> 00:38:35
We haven't talked about
kinetics yet, but low

591
00:38:35 --> 00:38:39
temperature also slows
the rate, which is bad.

592
00:38:39 --> 00:38:41
Because you not only want to
make a lot of your product, you

593
00:38:41 --> 00:38:45
want to make it in a reasonable
time frame and sell it and make

594
00:38:45 --> 00:38:47
lots of money and retire early.
 

595
00:38:47 --> 00:38:51
So you care about how fast the
reaction is going as well.

596
00:38:51 --> 00:38:55
So for an exothermic reaction
then, you have to balance out

597
00:38:55 --> 00:38:58
what's thermodynamically
favorable and what's

598
00:38:58 --> 00:39:00
kinetically favorable.
 

599
00:39:00 --> 00:39:04
So thermodynamically, you would
want a low temperature, but

600
00:39:04 --> 00:39:08
kinetically in terms of the
rate, that's not so good.

601
00:39:08 --> 00:39:12
So they use a compromised
temperature, which is 500

602
00:39:12 --> 00:39:15
degrees c, so that's
pretty high actually

603
00:39:15 --> 00:39:18
for this reaction.
 

604
00:39:18 --> 00:39:21
So what are other things that
you could do to drive this

605
00:39:21 --> 00:39:26
reaction toward products?
 

606
00:39:26 --> 00:39:27
So yeah, what's something
else you could do?

607
00:39:27 --> 00:39:31
STUDENT: Increase the volume.
 

608
00:39:31 --> 00:39:31
PROFESSOR: Right.
 

609
00:39:31 --> 00:39:33
So you could think
about volume here.

610
00:39:33 --> 00:39:39
So here we have four molecules
of gas on one side, and two

611
00:39:39 --> 00:39:42
molecules of gas on
the other side.

612
00:39:42 --> 00:39:48
So you can think about changing
that to favor your products.

613
00:39:48 --> 00:39:49
What is something
else you could do?

614
00:39:49 --> 00:39:51
STUDENT: Enzymes.
 

615
00:39:51 --> 00:39:56
PROFESSOR: Enzymes, we'll
talk about that in a minute.

616
00:39:56 --> 00:39:58
If you can't use the enzymes,
what's something else

617
00:39:58 --> 00:39:59
that you could do?
 

618
00:39:59 --> 00:40:02
STUDENT: You could remove
ammonia from the system.

619
00:40:02 --> 00:40:04
PROFESSOR: Yup, so you could
remove ammonia from the

620
00:40:04 --> 00:40:07
system, which would also
shift the direction.

621
00:40:07 --> 00:40:10
So let's just put those
two things down.

622
00:40:10 --> 00:40:11
Remove products.
 

623
00:40:11 --> 00:40:14
So if you remove ammonia from
the system, and they actually

624
00:40:14 --> 00:40:17
do this in the industrial
process, so they'll stop --

625
00:40:17 --> 00:40:21
they'll, at a certain time
points, they will remove the

626
00:40:21 --> 00:40:23
product and they'll say
hey, let's shift the

627
00:40:23 --> 00:40:24
reaction to make more.
 

628
00:40:24 --> 00:40:28
You just changed q versus k,
you removed your product, so

629
00:40:28 --> 00:40:31
now we want to shift to
minimize that stress

630
00:40:31 --> 00:40:33
and make more product.
 

631
00:40:33 --> 00:40:37
And the first response,
compress the volume, so we go

632
00:40:37 --> 00:40:41
from four molecules to two
molecules, and that would be

633
00:40:41 --> 00:40:44
favor -- again, the system
would want to respond, you

634
00:40:44 --> 00:40:49
compressed the volume, you
increased the pressure, so you

635
00:40:49 --> 00:40:53
want to respond in such a way
that compensates for that

636
00:40:53 --> 00:40:56
increased pressure, which is
decrease the pressure by going

637
00:40:56 --> 00:40:59
from the four molecules to two.
 

638
00:40:59 --> 00:41:01
So both of those are
great, and both of those

639
00:41:01 --> 00:41:03
are, in fact, used.
 

640
00:41:03 --> 00:41:06
Sometimes when you study
chemistry you'll realize that

641
00:41:06 --> 00:41:11
some of the -- people made a
lot of money on this, and

642
00:41:11 --> 00:41:13
that some of the principles
are actually very simple.

643
00:41:13 --> 00:41:16
You are learning principles
in this class that, applied

644
00:41:16 --> 00:41:19
correctly, could make
you a lot of money.

645
00:41:19 --> 00:41:21
Some of the scientific
discoveries are actually

646
00:41:21 --> 00:41:23
not all that complicated.
 

647
00:41:23 --> 00:41:26
All right.
 

648
00:41:26 --> 00:41:29
So someone said use enzymes.
 

649
00:41:29 --> 00:41:32
I love that answer, I want to
use enzymes to do a lot of

650
00:41:32 --> 00:41:35
those things, and people
are trying to do this.

651
00:41:35 --> 00:41:39
Now, why would you want
to use an enzyme?

652
00:41:39 --> 00:41:42
Well, there is a lot of
nitrogen in the air, but

653
00:41:42 --> 00:41:47
there's not a lot of usable
nitrogen, because n 2 gas is

654
00:41:47 --> 00:41:49
in the air, but it's very
difficult to break it

655
00:41:49 --> 00:41:52
apart to form ammonia.
 

656
00:41:52 --> 00:41:55
And when you think about
bonding, you can probably tell

657
00:41:55 --> 00:42:00
me why it's hard to break n 2
apart, and if you consider how

658
00:42:00 --> 00:42:04
many bonds would be between
those two nitrogens.

659
00:42:04 --> 00:42:08
So it's there but
it's hard to do.

660
00:42:08 --> 00:42:11
So the industrial process
that's used now pretty much is

661
00:42:11 --> 00:42:14
the same industrial process
that's been used for quite a

662
00:42:14 --> 00:42:18
while, the Haber-Bosch process,
which does not use enzymes.

663
00:42:18 --> 00:42:22
And here are some
pictures of these folks.

664
00:42:22 --> 00:42:28
This resulted in two Noble
prizes, the development of

665
00:42:28 --> 00:42:32
the industrial process here,
and it's still being used.

666
00:42:32 --> 00:42:37
On a historic note, these were
German scientists, and so,

667
00:42:37 --> 00:42:40
working out this process was
important to the Germans

668
00:42:40 --> 00:42:42
during World War II.
 

669
00:42:42 --> 00:42:47
It's still the process
going on today.

670
00:42:47 --> 00:42:49
So what about enzymes.
 

671
00:42:49 --> 00:42:52
Maybe enzymes could do a bit
better than this process.

672
00:42:52 --> 00:42:54
It's not true yet.
 

673
00:42:54 --> 00:42:58
Still the Haber-Bosch
industrial process is the

674
00:42:58 --> 00:43:02
one that's being used,
but enzymes can do it.

675
00:43:02 --> 00:43:07
So, some of the problems of a
lot of the common industrial

676
00:43:07 --> 00:43:10
reactions are that you use high
temperatures -- remember we

677
00:43:10 --> 00:43:12
said the compromised
temperature was 500

678
00:43:12 --> 00:43:14
degrees celsius.
 

679
00:43:14 --> 00:43:17
We were talking about
compressing the volume, so

680
00:43:17 --> 00:43:21
you want to put in energy
to compress that volume.

681
00:43:21 --> 00:43:24
And so that is expensive.
 

682
00:43:24 --> 00:43:27
And you might want to think
about a way, could you do that

683
00:43:27 --> 00:43:33
reaction at normal ambient
temperature without applying

684
00:43:33 --> 00:43:34
energy to the system.
 

685
00:43:34 --> 00:43:39
Well, enzymes can do this
reaction at ambient

686
00:43:39 --> 00:43:42
temperatures and they don't
have to have high pressure

687
00:43:42 --> 00:43:45
associated with them, and the
way the enzymes do this, and

688
00:43:45 --> 00:43:48
here's a little cartoon of a
space-filling model of

689
00:43:48 --> 00:43:52
a particular enzyme
called nitrogenase.

690
00:43:52 --> 00:43:56
So for nitrogen, and the
ase means it's an enzyme.

691
00:43:56 --> 00:44:00
And the secret to this enzyme,
how it can do what Haber and

692
00:44:00 --> 00:44:04
Bosch got two Nobel prizes for
-- this enzyme has received

693
00:44:04 --> 00:44:08
no Nobel prizes, and it
can do the same thing.

694
00:44:08 --> 00:44:11
Its secret are metals.
 

695
00:44:11 --> 00:44:15
It uses these clusters of
metals in the context of the

696
00:44:15 --> 00:44:20
protein environment to do this
chemistry, and they have iron,

697
00:44:20 --> 00:44:24
and they have also inorganic
sulfide, and molybdenum, and so

698
00:44:24 --> 00:44:29
these combinations of metals
can do this chemistry.

699
00:44:29 --> 00:44:31
And a number of scientists
have been working for decades

700
00:44:31 --> 00:44:35
now trying to understand
how the enzyme works.

701
00:44:35 --> 00:44:37
It's actually quite complicated
and it's been pretty

702
00:44:37 --> 00:44:39
controversial.
 

703
00:44:39 --> 00:44:42
So let me just kind of show you
at the heart of the enzyme,

704
00:44:42 --> 00:44:46
here all the atoms of the
enzyme, but if you rotate the

705
00:44:46 --> 00:44:50
enzyme around and go in, the
secret was that those

706
00:44:50 --> 00:44:52
combinations of metals.
 

707
00:44:52 --> 00:44:54
And one of the units that we're
going to have second to last in

708
00:44:54 --> 00:44:58
this courses is about
transition metals, that metals

709
00:44:58 --> 00:45:00
can do a lot of really
important things in biological

710
00:45:00 --> 00:45:03
systems, and also in industrial
processes and other

711
00:45:03 --> 00:45:06
things as well.
 

712
00:45:06 --> 00:45:10
So I do also like to
mention research is

713
00:45:10 --> 00:45:11
going on here at MIT.
 

714
00:45:11 --> 00:45:16
I've mentioned Dick Schrock
before, he won a Nobel Prize in

715
00:45:16 --> 00:45:21
chemistry a few years back, but
not for his work on sort of

716
00:45:21 --> 00:45:28
nitrogenase systems, but he was
able to design a small catalyst

717
00:45:28 --> 00:45:31
that can do this chemistry,
that can catalyze this

718
00:45:31 --> 00:45:34
reduction of nitrogen to
ammonia at a defined

719
00:45:34 --> 00:45:36
molybdenum center.
 

720
00:45:36 --> 00:45:38
Again, we'll talk about
transition metals

721
00:45:38 --> 00:45:39
later in the course.
 

722
00:45:39 --> 00:45:43
And so his laboratory is very
interested in coming up with

723
00:45:43 --> 00:45:49
better ways to split nitrogen
than the industrial processes

724
00:45:49 --> 00:45:50
that are currently used.
 

725
00:45:50 --> 00:45:53
Some people are studying
enzymes, other people are

726
00:45:53 --> 00:45:56
trying to use some of the tools
that come out the enzymes,

727
00:45:56 --> 00:46:00
thinking about the enzymes and
come up with other

728
00:46:00 --> 00:46:01
catalysts as well.
 

729
00:46:01 --> 00:46:04
So this work is going
on here at MIT.

730
00:46:04 --> 00:46:11
All right, so let's give one
more example of Le Chatelier

731
00:46:11 --> 00:46:15
from a biological perspective,
and this has to do with

732
00:46:15 --> 00:46:17
the following reaction.
 

733
00:46:17 --> 00:46:23
The combination of oxygen with
hemoglobin in your blood.

734
00:46:23 --> 00:46:27
And the reaction here, we have
hemoglobin plus oxygen has

735
00:46:27 --> 00:46:33
oxyhemoglobin, so the oxygen is
now bound to be hemoglobin.

736
00:46:33 --> 00:46:36
This reaction is very
important for you.

737
00:46:36 --> 00:46:40
None of us would be alive
if this was not happening.

738
00:46:40 --> 00:46:46
We need to get the oxygen
from our lungs to our cells.

739
00:46:46 --> 00:46:49
So what happens if you
decide to climb Mount

740
00:46:49 --> 00:46:51
Everest, for example.
 

741
00:46:51 --> 00:46:55
You may be thinking how hard
can that be after a first

742
00:46:55 --> 00:46:57
semester freshman year at MIT.
 

743
00:46:57 --> 00:47:02
Really, I can think
more broadly about it.

744
00:47:02 --> 00:47:06
All right, how many of you have
climbed a mountain so far?

745
00:47:06 --> 00:47:07
Woah, a lot of people.
 

746
00:47:07 --> 00:47:10
OK, something about going to
MIT and climbing big mountains

747
00:47:10 --> 00:47:12
seems to be connected.
 

748
00:47:12 --> 00:47:15
How many people feel like after
surviving the first year, why

749
00:47:15 --> 00:47:17
not, go ahead and
climb a mountain?

750
00:47:17 --> 00:47:18
Any more people?
 

751
00:47:18 --> 00:47:20
OK, no.
 

752
00:47:20 --> 00:47:24
So you gotta -- you've been
through the hard part now,

753
00:47:24 --> 00:47:26
you don't want to risk
anything anymore.

754
00:47:26 --> 00:47:29
All right, so this slide seems
to be cutting off some stuff,

755
00:47:29 --> 00:47:31
so let's look over here.
 

756
00:47:31 --> 00:47:34
So what happens to
this reaction?

757
00:47:34 --> 00:47:38
Well, as you go up higher
and higher, the partial

758
00:47:38 --> 00:47:40
pressure of oxygen changes.
 

759
00:47:40 --> 00:47:47
So you're going to drop in
partial pressure 0.2 to 0.14 .

760
00:47:47 --> 00:47:51
So what happens to
this reaction if this

761
00:47:51 --> 00:47:54
value decreases?
 

762
00:47:54 --> 00:47:59
What happens, what
direction does it shift?

763
00:47:59 --> 00:48:03
For products or reactants?
 

764
00:48:03 --> 00:48:03
Right.
 

765
00:48:03 --> 00:48:08
So, if this is going down,
then some of your oxygenated

766
00:48:08 --> 00:48:12
hemoglobin is going to
a release its oxygen.

767
00:48:12 --> 00:48:15
So it'll respond in such
a way to compensate

768
00:48:15 --> 00:48:20
for that added stress.
 

769
00:48:20 --> 00:48:23
So what can you do to switch
it back the other way?

770
00:48:23 --> 00:48:26
Again, we want our blood
to be oxygenated.

771
00:48:26 --> 00:48:30
What happens to compensate
for this if you're going

772
00:48:30 --> 00:48:34
to climb a mountain?
 

773
00:48:34 --> 00:48:37
What happens in the body?
 

774
00:48:37 --> 00:48:37
Yeah.
 

775
00:48:37 --> 00:48:41
STUDENT: The body can
produce more hemoglobin.

776
00:48:41 --> 00:48:41
PROFESSOR: The body can
produce more hemoglobin.

777
00:48:41 --> 00:48:44
So you often go to another
altitude and hang out

778
00:48:44 --> 00:48:47
for a while before you
start going way up.

779
00:48:47 --> 00:48:51
And what's happening during
that time is your body realizes

780
00:48:51 --> 00:48:54
there is a problem, it knows
about the Le Chatelier's

781
00:48:54 --> 00:48:58
principle, and so it's going
to make more hemoglobin.

782
00:48:58 --> 00:49:02
And if you add more hemoglobin
to this reaction, what

783
00:49:02 --> 00:49:06
direction does it go?
 

784
00:49:06 --> 00:49:10
Toward products, right.
 

785
00:49:10 --> 00:49:11
OK.
 

786
00:49:11 --> 00:49:18
So I wanted to mention
significant figures, and there

787
00:49:18 --> 00:49:22
is -- I have to make a
confession that when I first

788
00:49:22 --> 00:49:26
started teaching this course, I
had never really paid attention

789
00:49:26 --> 00:49:28
to the rules of significant
figures for logs.

790
00:49:28 --> 00:49:31
In this unit, the next unit,
the unit after, you get the

791
00:49:31 --> 00:49:34
idea, there are going to be a
lot of logs, and they

792
00:49:34 --> 00:49:38
have special rules for
significant figures.

793
00:49:38 --> 00:49:40
So in the bottom of your
handout, these rules

794
00:49:40 --> 00:49:43
are explained, it's
also in your book.

795
00:49:43 --> 00:49:44
Pay attention to this.
 

796
00:49:44 --> 00:49:48
It's going to help you
on all the problem-sets

797
00:49:48 --> 00:49:49
and in the course.
 

798
00:49:49 --> 00:49:54
So I just wanted to point
out special rules about

799
00:49:54 --> 00:49:56
significant figures for logs.
 

800
00:49:56 --> 00:50:01
All right, that's it for
today, see you on Wednesday.

801
00:50:01 --> 00:50:02