Q: For the reaction $$Q \rightarrow 2R$$, which is second order in $$Q$$, if $$[Q]_0 = 0.010\,M$$ and $$[Q] = 0.0010\,M$$ after $$500$$ seconds, what is the rate constant $$k$$?

$$2.2 \times 10$$^{-5}$$\,M$$^{-1}$$s^{-1}$

Question 1

Which of the following best describes the difference between average and instantaneous reaction rates?

Accepted Answer

Average rate is calculated using concentrations at the beginning and end of a time period, while instantaneous rate is determined by the slope of a tangent to the concentration vs. time curve at a specific time.

Question 2

For the reaction $$2NH_3 \rightarrow 3N_2 + H_2$, which expression correctly relates the rates of change of the concentrations of the reactants and products?

Accepted Answer

$$-\frac{1}{2} \frac{d[NH_3$]}{dt} = \frac{1}{3} \frac{d[N_2$]}{dt} = \frac{1}{1} \frac{d[H_2$]}{dt}$$

Question 3

A reaction is found to have a rate law $$	ext{rate} = k[A]^2[B]. $$What is the overall order of the reaction?

Accepted Answer

3

Question 4

Which factor does NOT affect the rate of a chemical reaction?

Accepted Answer

Color of the reactants

Question 5

Consider the reaction $$A \rightarrow B. If $$the concentration of $$B$$ increases from $$0.034\,M to$$ $$0.083\,M in$$ $$14.8$$ seconds, what is the average rate of the reaction?

Accepted Answer

$$0.0033\,M/s$$

Question 6

Which of the following statements about the rate constant $$k is $$TRUE?

Accepted Answer

$$k is $$specific for a particular reaction at a particular temperature.

Question 7

For a first-order reaction, what is the formula for the half-life?

Accepted Answer

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

Question 8

Which scenario best illustrates the effect of surface area on reaction rate?

Accepted Answer

Iron powder reacts faster with acid than a block of iron.

Question 9

The Arrhenius equation relates the rate constant $$k to $$which two factors?

Accepted Answer

Activation energy and temperature

Question 10

A reaction mechanism consists of the following steps:
Step 1: $$NO(g) + Cl_2$(g) \rightleftharpoons $$NOCl_2$$(g) ($$fast)
Step 2: $$NOCl_2(g) + NO(g$$) \rightarrow 2NOCl(g)$$ (slow)
Which step determines the rate law for the overall reaction?

Accepted Answer

Step 2

Question 11

Which of the following is a correct rate law for a bimolecular elementary reaction?

Accepted Answer

$$	ext{rate} = k[A][B]$$

Question 12

Which statement about catalysts is TRUE?

Accepted Answer

Catalysts provide an alternate pathway with lower activation energy.

Question 13

For the reaction $$Q \rightarrow 2R$$, which is second order in $$Q$$, if $$[Q]_0 = 0.010\,M$$ and $$[Q] = 0.0010\,M$$ after $$500$$ seconds, what is the rate constant $$k$$?

Accepted Answer

$$2.2 	imes 10$$^{-5}$$\,M$$^{-1}$$s^{-1}$

Question 14

Which of the following best explains why increasing temperature generally increases the rate of a chemical reaction?

Accepted Answer

Higher temperature increases the fraction of molecules with kinetic energy greater than the activation energy.

Question 15

Which of the following is NOT a requirement for a valid reaction mechanism?

Accepted Answer

The mechanism must prove the existence of all intermediates.

Question 16

Which of the following is a characteristic of a zero-order reaction?

Accepted Answer

The rate is independent of the concentration of reactant.

Question 17

Which of the following best describes the role of enzymes in biological reactions?

Accepted Answer

Enzymes orient substrates for reaction and lower the activation energy.

Question 18

In the lock-and-key model of enzyme activity, what is the relationship between the enzyme's active site and the substrate?

Accepted Answer

The active site is a perfect fit for the substrate.

Question 19

Which of the following is an example of a reaction intermediate?

Accepted Answer

A product that is formed and consumed in different steps of a mechanism.

Question 20

Which step in a multi-step reaction mechanism is the rate-determining step?

Accepted Answer

The step with the largest activation energy and slowest rate.

Chapter 17: Chemical Kinetics – Reaction Rates and Mechanisms

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