Q: A plot of $$\ln k$$ versus $$1/T$$ for a reaction yields a straight line with a slope of $$-1.12 \times 10^4$. What is the activation energy E_a$ in J/mol? (Use R = 8.314$$\ \mathrm{J/(mol\cdot K)}$$)

$$E_a = (1.12 \times 10^4$) \times 8.314 = 93,117\ \mathrm{J/mol}$$

Q: In the catalyzed decomposition of $$\mathrm{H_2O_2} by$$ $$\mathrm{I^-}$$, what is the expected rate law based on the slow step: $$\mathrm{H_2O_2 + I^- \rightarrow H_2O + IO^-}$$?

$$\text{Rate} = k[H_2O_2][I^-]$$

Question 1

Which of the following best explains why the reaction between sodium and bromine (as shown in the first image) occurs much faster than the rusting of iron?

Accepted Answer

The reaction between sodium and bromine has a much higher rate constant $$k$$ due to a lower activation energy and more favorable collision conditions.

Question 2

Given the data in the second image, what is the average rate of disappearance of $$\mathrm{H_2$}$$ between 20 and 30 seconds?

Accepted Answer

$$0.0121\ \mathrm{M/s}$$

Question 3

For the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightarrow 2 HI(g)}$$, if the rate of disappearance of $$\mathrm{H_2$} is$$ $$0.0121\ \mathrm{M/s}$$, what is the rate of appearance of $$\mathrm{HI}$$?

Accepted Answer

$$0.0242\ \mathrm{M/s}$$

Question 4

Which of the following rate laws corresponds to a reaction that is first order with respect to $$[A]$$?

Accepted Answer

$$	ext{Rate} = k[A]$$

Question 5

A reaction is found to have the following initial rates: $$[A] = 0.10\ \mathrm{M}$$, rate $$= 0.015\ \mathrm{M/s}$$; $$[A] = 0.20\ \mathrm{M}$$, rate $$= 0.030\ \mathrm{M/s}$$; $$[A] = 0.40\ \mathrm{M}$$, rate $$= 0.060\ \mathrm{M/s}. $$What is the order of the reaction with respect to $$A$$?

Accepted Answer

First order

Question 6

For a first-order reaction, which of the following plots will yield a straight line?

Accepted Answer

$$\ln[A] vs$$. $$t$$

Question 7

A first-order reaction has a rate constant $$k = 0.0214\ \mathrm{min}^{-1}. $$What is the half-life of the reaction?

Accepted Answer

$$t_{1/2} = \dfrac{0.693}{k}$$

Question 8

For a second-order reaction $$A \rightarrow$$ products, what is the integrated rate law?

Accepted Answer

$$\dfrac{1}{[A]_t} = kt + \dfrac{1}{[A]_0}$$

Question 9

Which of the following statements about the half-life of a second-order reaction is correct?

Accepted Answer

The half-life increases as $$[A]_0$$ decreases.

Question 10

The Arrhenius equation is $$k = Ae$$^{-E_a/RT}$$. If the activation energy E_a$ increases, what happens to the rate constant k$ (assuming all other factors remain constant)?

Accepted Answer

$$k$$ decreases

Question 11

A plot of $$\ln k$$ versus $$1/T$$ for a reaction yields a straight line with a slope of $$-1.12 	imes 10^4$. What is the activation energy E_a$ in J/mol? (Use R = 8.314$$\ \mathrm{J/(mol\cdot K)}$$)

Accepted Answer

$$E_a = (1.12 	imes 10^4$) 	imes 8.314 = 93,117\ \mathrm{J/mol}$$

Question 12

Which of the following is a correct statement about the effect of temperature on reaction rate?

Accepted Answer

Increasing temperature increases the fraction of molecules with energy greater than $$E_a.$$

Question 13

Which of the following best describes a catalyst's effect on a chemical reaction?

Accepted Answer

A catalyst provides an alternative pathway with a lower activation energy.

Question 14

In the catalyzed decomposition of $$\mathrm{H_2O_2} by$$ $$\mathrm{I^-}$$, what is the expected rate law based on the slow step: $$\mathrm{H_2O_2 + I^- \rightarrow H_2O + IO^-}$$?

Accepted Answer

$$	ext{Rate} = k[H_2O_2][I^-]$$

Question 15

Which of the following is an example of a heterogeneous catalyst?

Accepted Answer

Platinum in a catalytic converter for car exhaust

Question 16

A reaction mechanism consists of the following steps:
Step 1: $$\mathrm{NO_2$ + NO_2$ \rightarrow NO + NO_3$} ($$slow)
Step 2: $$\mathrm{NO_3$ + CO \rightarrow NO_2$ + CO_2$} ($$fast)
What is the expected rate law for the overall reaction?

Accepted Answer

$$	ext{Rate} = k[NO_2$]^2$$

Question 17

Which of the following statements about reaction intermediates is correct?

Accepted Answer

Intermediates are produced in one step and consumed in a later step of the mechanism.

Question 18

For a reaction with the rate law $$	ext{Rate} = k[A][B]$$, what is the overall order of the reaction?

Accepted Answer

Second order

Question 19

Which of the following changes will NOT increase the rate of a chemical reaction?

Accepted Answer

Decreasing the temperature

Chapter 15: Chemical Kinetics – Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards