AP Chemistry 2.1 Chemical Reaction Rates

AP Chemistry 2.1 Chemical Reaction Rates. Which of the following is true according to the reaction profile?

APAP Chemistry
AP ChemistryChemical Reaction Rates
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Transcript

00:15

And here are your potential answers: Okay, so though it may just look like a random [Boy drawing]

00:22

squiggle a kindergartener drew, what you’re looking at is actually our reaction profile

00:27

curve, the focus of today’s problem.

00:30

Figure out what the deal with this curve is and we figure out the problem.

00:33

If only that was the way all problems in life worked… [Woman discussing problems with a reaction curve]

00:36

Believe it or not, a reaction profile isn’t the side view of a reaction.

00:40

It’s a graphical representation of the energy pathway through a chemical reaction. [Example of a reaction profile graph]

00:45

The horizontal axis shows the reaction progress, which means how close the reaction is to completion.

00:53

Just like in a chemical reaction equation, the left side of this graph represents the

00:58

reactants, and the right side represents the products. [Graph showing reactants and products of a reaction]

01:00

So as long as you’re used to reading left-to-right, it should be pretty easy.

01:05

Sorry, manga enthusiasts and Hebrew-speakers.

01:07

Anyway, the vertical axis is the energy of the reactant and product species.

01:13

You can think of it as the species in this reaction riding that curve like a roller coaster [People riding a roller-coaster]

01:18

as they’re transformed from the reactants into the products.

01:21

Woo!

01:22

Hope you didn’t eat a big lunch.

01:25

Since there are two humps here, we know that the reaction occurs in two steps. [Two humps of reaction curve highlighted]

01:29

And that maybe the kindergartner who drew this doodle is a camel-lover.

01:32

Anyway, the three local minima represent the reactants, intermediates, and products.

01:38

Each local maximum represents a transition state.

01:42

So let’s dive back into those answers. [People dive into a river]

01:45

Is this an endothermic reaction?

01:47

An endothermic reaction is a reaction that absorbs energy as heat from the surroundings.

01:52

From the reaction profile curve, we can see that the energy of the products is lower than

01:56

the energy of the reactants.

01:59

That means that the reaction releases energy into the surroundings in the form of heat. [Exothermic reaction definition]

02:04

Which means two things: It’s great to take on ski trips, AND it’s

02:07

exothermic, not endothermic.

02:08

So we can give option B the cold shoulder. [Letter B zapped and frozen]

02:12

Is the first step of the reaction the rate-determining step?

02:15

Well, out of this reaction’s two steps, the rate-determining step will be the one

02:19

that has the highest activation energy barrier to overcome.

02:24

The barrier to the first step is the difference in energy between the reactants and the first

02:28

transition state.

02:30

The barrier to the second step is the difference in energy between the intermediates and the

02:35

second transition state.

02:37

In this case, the second barrier is larger, so the second step is rate-determining. [Finger points to second transition state]

02:40

Looks like we’ve just determined that option C is not our guy.

02:45

How about D?

02:46

Was a catalyst used to decrease the activation energy of the reaction? [Catalyst in court with a judge]

02:50

Well, we have no way to tell whether a catalyst was already involved in this reaction or not.

02:55

Not enough information, not our answer.

02:57

So that means that A - “There is an intermediate formed in the reaction,” is the correct

03:04

answer.

03:05

We figured that out like a minute ago, but it’s good to consider the other options

03:07

just to be sure.

03:08

Well…that and we didn't have any other cool plans for today, and we figured we'd force [Two guys sitting on a sofa]

03:11

you to spend more time with us.

03:12

That's what friends do, right?

03:13

…Right?