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AP Chemistry 3.2 Chemical Reaction Rates 6 Views


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AP Chemistry 3.2 Chemical Reaction Rates. What is the experimental rate law for the reaction?

Language:
English Language

Transcript

00:04

Here’s your Shmoop du jour, brought to you by experimental rate law, the rule that made

00:09

all speed limits Avogadro’s number for a day. [Policeman pointing to speed limit with Avogadro's number on it]

00:12

It wasn’t popular.

00:13

Anyway, here’s today’s question:

00:15

What is the experimental rate law for the following reaction, given the data below?

00:20

And here are your potential answers: Anybody feeling psychic? [Psychic woman appears]

00:27

Let’s start off by trying to predict what that rate law should be based on the reaction [Stoichiometry appears on her crystal ball]

00:31

stoichiometry.

00:33

So the stoichiometric coefficients are often the same as the reaction

00:37

order for each reactant. [Man working in a science lab]

00:39

Since the reactants are two CO and one O2, the reaction will probably be second order [Finger points to the reactants in the equation]

00:44

in CO and first order in O2.

00:47

If this guess is correct, the rate equals the

00:50

rate constant times the concentration of carbon monoxide squared times the concentration of [Psychic woman holding the rate constant]

00:56

oxygen, which is answer (B).

00:58

Shh…something is telling us we should open a psychic hotline…call now…only $10 a [Psychic woman doing a phone line advert]

01:03

minute…

01:04

But unfortunately, this isn’t a guessing game.

01:06

To test our hypothesis, we’ll need to look at the table. [Wheel of fortune presenter chucks away his microphone and walks off]

01:09

Between experiments 1 and 2, the initial concentration of CO is doubled while the initial concentration

01:15

of O2 stays the same. [Man pointing to figures in a table]

01:17

These two data points show us how the rate depends on the concentration of CO without

01:22

the influence of O2.

01:23

Seriously, no peer pressure here.

01:25

In this case, when the CO concentration is doubled, the rate increases by a factor of

01:30

four, which means the rate varies with concentration of CO squared. [Person using a pipette in a lab]

01:36

Between experiments 1 and 3, the initial concentration of O2 is doubled while the concentration of

01:40

CO stays the same.

01:42

We can use these two data points to figure out how the rate depends on the concentration

01:45

of O2 without worrying about CO.

01:47

Here, we see that when the O2 concentration is doubled, the reaction rate is also doubled,

01:52

so the rate is proportional to the O2 concentration. [Person taking blue liquid out of a flask]

01:55

Putting this all together, our overall rate law is rate = k[CO]2 [O2] the rate equals [Man pointing to a blackboard with the answers on]

01:59

the rate constant times the concentration of carbon monoxide squared times the concentration

02:04

of oxygen.

02:05

And, hey…that sounds pretty familiar, which means our guess was right and B is the correct [Psychic woman looks happy]

02:10

answer.

02:11

All right, well, this was fun, but we gotta get this hotline set up…shh…the spirits

02:16

are speaking…they're telling you to phone in and stay on the line for an hour…. [Psychic hotline ad]

02:21

on your parents credit card... yes, 1-800 shmoop, we'll tell you your future...

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