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AP Chemistry 2.5 Laws of Thermodynamics 8 Views


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Description:

AP Chemistry 2.5 Laws of Thermodynamics. Which of the following is true for a reaction at equilibrium?

Language:
English Language

Transcript

00:04

And here's your Shmoop du jour, brought to you by equilibrium, the human rights movement [People protesting outside a library]

00:08

that insists librarians should be treated equally.

00:12

Okay, here's our question.

00:14

Which of the following is true for a reaction at equilibrium?

00:19

And here are your potential answers.

00:20

Okay, don’t get all “one with nature” on us here…we’re talking about molecular [Boy balancing books on his head]

00:26

equilibrium here.

00:28

That is, the point at which the forward rate of a reversible chemical reaction equals the

00:33

reverse rate. [Equilibrium of reaction depicted on a graph]

00:35

The concentrations of reactants and products don’t change, even though reactions are

00:38

still taking place.

00:41

So A and B make C and D at the same rate that C and D make A and B.

00:47

You thinking what we’re thinking? [Two guys jumping up and down]

00:48

Great, let's say it together.

00:50

3, 2, 1…Bananas!

00:53

…Oh.

00:54

Or example time.

00:55

That's good, too.

00:56

Okay, imagine that there’s a team of mathletes who decide that they should socialize more. [Mathletes socialising with each other]

01:03

So they schedule a hang-out sesh with the science Olympiad team studying next door.

01:07

We're sensing this is going to end in a rager. [Mathletes and Science Olympians together]

01:10

…Just us?

01:11

At some point, the students are split among the rooms, and the rate at which a mathlete

01:15

leaves his room is the same as the rate at which a different mathlete enters. [Mathletes leaving and entering the rooms]

01:21

The same is true for the science Olympians.

01:23

This smarty-swap can be thought of as our “reaction.”

01:27

The relative “concentration” of mathletes and science Olympians remains the same, despite

01:33

the fact that there’s still movement and different individuals might be present at [Olympians and Mathletes interchanging between rooms]

01:36

any given time.

01:38

And here we have achieved the ultimate nerdy equilibrium.

01:41

Hm.

01:42

Really thought it would end in a rager.

01:44

So let’s take another look at our question. [Boy using binoculars]

01:47

What do all these variables mean?

01:49

Well, DeltaH - or change in enthalpy - tells us if a reaction absorbs or releases

01:55

heat.

01:56

DeltaG, or the change in Gibbs free energy, tells us if a reaction is spontaneous

02:03

or non-spontaneous.

02:05

And DeltaS, or the change in entropy, tells us if a reaction leads to more or less [Delta H, G and S definitions]

02:10

disorder.

02:11

Of the science-y kind, not the mental kind. [Boy spinning a basketball on his finger]

02:14

Though too much chemistry will give the best of us anxiety.

02:17

Option A just means the reaction releases heat. [Girl cooking marshmallows on a fire]

02:19

It doesn’t tell us anything about equilibrium.

02:22

Option C tells us that there is no entropy change.

02:25

This just means that the degree of disorder remains the same.

02:29

Option D implies that there is no heat absorbed or released from the reaction.

02:32

All right, Option B. Not to Obi Wan you, but you’re our only hope. [Obi Wan appears and prods option B]

02:38

This option is all about spontaneity.

02:40

We know that if DeltaG<0, the reaction is spontaneous, and if DeltaG>0, the reaction is not spontaneous.

02:48

But what if DeltaG equals zero? [Boys walking a tight rope together]

02:50

This means the reaction is at equilibrium, and forward and reverse rates are the same.

02:54

So B is the right answer.

02:56

And there you have it folks, equilibrium.

02:57

Now let’s check on our smarty-pants party before somebody blows up a Bunsen burner. [Olympians and Mathletes socialising together in classrooms]

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