Q: Which of the following equations correctly expresses the average rate of disappearance of reactant A in the reaction $$A \rightarrow B$$?

$$\text{Average rate} = -\frac{\Delta [A]}{\Delta t}$$

Q: For the reaction $$2HI(g) \rightarrow H_2$(g) + I_2$(g)$$, which of the following correctly relates the rates of disappearance and appearance of the species?

$$\text{Rate} = -\frac{1}{2}\frac{\Delta [HI]}{\Delta t} = \frac{\Delta [H_2$]}{\Delta t} = \frac{\Delta [I_2$]}{\Delta t}$$

Q: A reaction has an activation energy ($$E_a) of 100 kJ/$$mol and is run at 300 K. Using the equation $$f = e$$^{-E_a/RT}$$, what is the fraction of molecules with energy greater than or equal to E_a$? (Use R = 8.314$ J/mol·K)

$$f = e$$^{-100,000/(8.314 \times 300)}$$

Q: For the reaction $$A \rightarrow B$$, the concentration of A decreases from 1.00 mol to 0.54 mol in 20 seconds. What is the average rate of appearance of B over this time interval?

$$\frac{0.46\ \text{mol}}{20\ \text{s}} = 0.023\ \text{mol/s}$$

Question 1

Which of the following best explains why a powdered medicine dissolves and acts faster in the stomach than the same medicine in tablet form?

Accepted Answer

Powdered medicine has a larger surface area, allowing for more immediate interaction with stomach fluids.

Question 2

A reaction is carried out with steel wool in air (20% O2) and then in pure O2 (100%). The reaction is much faster in pure O2. What factor is primarily responsible for this difference?

Accepted Answer

The increased concentration of O2 increases the frequency of collisions between reactant molecules.

Question 3

Which of the following equations correctly expresses the average rate of disappearance of reactant A in the reaction $$A \rightarrow B$$?

Accepted Answer

$$	ext{Average rate} = -\frac{\Delta [A]}{\Delta t}$$

Question 4

For the reaction $$2HI(g) \rightarrow H_2$(g) + I_2$(g)$$, which of the following correctly relates the rates of disappearance and appearance of the species?

Accepted Answer

$$	ext{Rate} = -\frac{1}{2}\frac{\Delta [HI]}{\Delta t} = \frac{\Delta [H_2$]}{\Delta t} = \frac{\Delta [I_2$]}{\Delta t}$$

Question 5

A reaction has the rate law $$	ext{Rate} = k[NH_4$^+][NO_2$^-]. If $$the concentration of $$NH_4$$^+$$ is doubled while NO_2$^- is $$kept constant, what happens to the rate?

Accepted Answer

The rate doubles.

Question 6

Given the following data for the reaction $$2NO(g) + 2H_2(g) ightarrow N_2$(g) + 2H_2O(g)$$:

Experiment 1: [NO] = 0.10 M, [H2] = 0.10 M, Rate = $$1.23 	imes 10$$^{-3}$$ M/s
Experiment 2: [NO] = 0.10 M, [H2] = 0.20 M, Rate = 2.46$$ 	imes $$10^{-3} M/s
$$Experiment 3: [NO] = 0.20 M, [H2] = 0.10 M, Rate = $$4.92 	imes 10$$^{-3}$$ M/s

What is the order of the reaction with respect to NO?

Accepted Answer

Second order

Question 7

For a first-order reaction, which of the following is the correct integrated rate law?

Accepted Answer

$$\ln [A]_t = -kt + \ln [A]_0$$

Question 8

The half-life of a first-order reaction is given by which of the following expressions?

Accepted Answer

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

Question 9

A reaction has an activation energy ($$E_a) of 100 kJ/$$mol and is run at 300 K. Using the equation $$f = e$$^{-E_a/RT}$$, what is the fraction of molecules with energy greater than or equal to E_a$? (Use R = 8.314$ J/mol·K)

Accepted Answer

$$f = e$$^{-100,000/(8.314 	imes 300)}$$

Question 10

Which of the following statements about catalysts is TRUE?

Accepted Answer

Catalysts increase the rate of a reaction by lowering the activation energy.

Question 11

In a multistep reaction mechanism, what is the rate-determining step?

Accepted Answer

The slowest elementary step in the mechanism.

Question 12

Which of the following best describes a reaction intermediate?

Accepted Answer

A species that is formed in one step of a reaction mechanism and consumed in a subsequent step.

Question 13

For the reaction $$A \rightarrow B$$, the concentration of A decreases from 1.00 mol to 0.54 mol in 20 seconds. What is the average rate of appearance of B over this time interval?

Accepted Answer

$$\frac{0.46\ 	ext{mol}}{20\ 	ext{s}} = 0.023\ 	ext{mol/s}$$

Question 14

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 enough energy to overcome the activation energy barrier.

Question 15

Which of the following is the correct form of the Arrhenius equation relating the rate constant $$k to $$temperature $$T$$?

Accepted Answer

$$k = A e$$^{-E_a/RT}$$

Question 16

Which of the following best describes the lock-and-key model of enzyme catalysis?

Accepted Answer

The substrate fits into the enzyme's active site like a key fits into a lock, allowing the reaction to proceed.

Question 17

Which of the following is a characteristic of a heterogeneous catalyst?

Accepted Answer

It exists in a different phase than the reactants and often provides a surface for the reaction to occur.

Question 18

If a reaction is first order in A and second order in B, what are the units of the rate constant $$k$$?

Accepted Answer

$$	ext{M}^{-2}	ext{s}^{-1}$$

Question 19

Which of the following is NOT a factor that affects the rate of a chemical reaction?

Accepted Answer

The color of the reactants

Chemical Kinetics: Factors Affecting Reaction Rates, Rate Laws, and Catalysis

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