Describe each of the following statements as true or false....

Describe each of the following statements as true or false. If false, rewrite the sentence to make it correct. (a) The rate-determining elementary step in a reaction is the slowest step in a mechanism. (b) It is possible to change the rate constant by changing the temperature. (c) As a reaction proceeds at constant temperature, the rate remains constant. (d) A reaction that is third order overall must involve more than one step.

Describe each of the following statements as true or false. If false, rewrite the sentence to make it correct.
(a) The rate-determining elementary step in a reaction is the slowest step in a mechanism.
(b) It is possible to change the rate constant by changing the temperature.
(c) As a reaction proceeds at constant temperature, the rate remains constant.
(d) A reaction that is third order overall must involve more than one step.

Key Concepts

Rate-determining Step

This is the slowest step in a multi-step reaction mechanism that controls the overall reaction rate. It’s a key concept in chemical kinetics because it limits how fast the overall reaction occurs, assuming that subsequent or preceding steps are faster, even though real mechanisms may have additional complexities.

Temperature Dependence of the Rate Constant

This concept relates to the fact that the rate constant of a reaction is dependent on temperature. According to the Arrhenius equation, the rate constant typically increases as the temperature rises due to an increase in the number of molecules possessing the necessary activation energy.

Reaction Rate and Concentration Dependence

While the rate constant is fixed at a given temperature, the reaction rate itself is a function of reactant concentrations. As reactants are consumed during the reaction, their decreasing concentrations usually cause the reaction rate to change, even if the temperature remains constant.

Overall Reaction Order versus Reaction Mechanism

Overall reaction order is determined from the rate law of a reaction and indicates how the rate depends on reactant concentrations. It does not directly reveal the number of steps in the reaction mechanism; a third order rate law can be observed in both one-step (elementary) and multi-step reactions, underscoring that reaction order is not a direct measure of mechanistic complexity.

Transcript

00:01 So let's go through these one by one.

00:04 But first, the rate determining step, which i'm going to say as rds, is by definition, the slow step.

00:13 This is just an absolutely fundamental idea of kinetics.

00:17 And it makes sense to the standpoint of, like, for instance, let's say you're going, you're taking a road trip from new york to california.

00:26 So it's a long road trip.

00:27 If you can, you know, let's say there's two steps.

00:30 The first step is get in the car, and the second step is drive.

00:36 If you go really, really fast in the running to the car, you bust it there, and then you drive, you know, 30 miles an hour all the way to california, it's going to take you forever.

00:46 No, it doesn't matter how fast you ran to the car.

00:49 But, you know, you can dilly -dally all the way to getting to the car and then drive, you know, 80 miles an hour all the way across.

00:55 And that's what's going to make a difference in the rate.

00:58 In other words, the faster steps are just, they happen so much faster that even if the way they play in effect on the rate of the reaction is just so minimal compared to the one slow step.

01:10 In this case, driving all the way across.

01:12 It's a long, longest step.

01:14 And so that's why the rate determining step is always the slow step.

01:19 That is by definition, remember that.

01:22 Next, this is the relationship between asking about the relationship between k and t.

01:28 And so this is defined by the uranus equation, smart guy figured it out.

01:33 K equals a, e to the negative ea over rt, where a is just a constant that's related to the reaction.

01:40 And you can see here, you might have to work through the math, pause the video if you need to, but if you increase the temperature, this whole exponent becomes smaller, which means it's less negative, meaning that this becomes a greater value and k increases.

01:56 So long story short, k increases as temperature increases, and that's what they're asking you.

02:02 And so this is true...

Please give Ace some feedback