Chapter 14 Practice Test

Question 1

Hydrofluoric acid is a weak acid with an equilibrium constant (at 25°C) of Ka = 7.2 x 10^-4 . What is the pH of a 1.00 M solution of this acid?

Answer 1

1.57

Question 2

Using the graph below, calculate the instantaneous reaction rate for the formation of NO at 100.0 s, and tell whether the instantaneous rate at 100.0 s is faster or slower than the instantaneous rate at 50.0 s.

Answer 2

1.34 × 10^−4 M / s, slower at 100s

Question 3

Mercury(II) chloride (HgCl2 ) reacts with oxalate ions (C2O42− ) according to the following equation.

2HgCl2(aq) + C2O42− (aq) → 2Cl − (aq) + 2CO2(g) + Hg2Cl2(s)

If Δ[CO2 ] / Δt = 5.2 × 10−7 M / s,
what is the value of Δ[C2O42− ] / Δt at the
same instant?

Answer 3

−2.6 × 10^−7 M / s

Question 4

Chlorine gas(Cl2 ) reacts with fluorine gas (F2 ) according to the following equation.

Cl2(g) + 3F2(g) → 2ClF3(g)

Suppose you combine one mole of Cl2 with three moles of F2, and then made a graph of the concentration of the reactants and the products versus time. Which of the following statements would be true of the graph at time = t ?

Answer 4

The slope of the curve for ClF3 will equal twice the rate of the reaction.

Question 5

Suppose you are studying the following reaction.

2A + B → 2C + D

You gather the following initial rate data for the reaction:

What will be the rate of formation of C when [A] is 0.040 M and [B] is 0.040 M?

Answer 5

0.084 M / s

Question 6

Suppose you are studying the following reaction:

2A + 2B → C + 2D

You find that when you double the concentration of A while keeping the concentration of B fixed, the rate of the reaction increases by a factor of 2. What conclusion can you draw about the rate law of this reaction?

Answer 6

The rate law is first order in [A].

Question 7

The following data are gathered for the radioactive decay of flourine-20

Time 0.0 2.0 4.0 6.0
Concentration 0.24 0.21 0.18 0.16

If the decay of 20F is a first-order reaction, which of the following is the best estimate of its half-life

Answer 7

10 s

Question 8

Consider the following first-order reaction.

A → B + C

The half-life of this reaction is 6.40 hours. Suppose you define the third-life (t1/3 ) of the reaction as the time at which one-third of the original amount of A remains. What is t1/3 for this reaction?

Answer 8

10 hours

Question 9

The reaction 2D -> 2E + F is second order in [D] and second order overall. The rate constant of this reaction at a particular temperature is 4.88 * 10^-3 M^-1s^-1. If the initial concentration of D is 1.95 M, what will be the rate of reaction a t = 900 s?

Answer 9

5.69 × 10^−5 M / s

Question 10

Suppose you are studying the following pair of reactions.

A → D + E
2B → D + E

The first reaction is first order in [A] and first order overall with a rate constant of 0.30 s−1. The second reaction is second order in [B] and second order overall with a rate constant of 0.30 M −1s−1. If [A]0 = [B]0 = 0.10 M, how much longer will the half-life of the second reaction be than the half-life of the first reaction at t = 0?

Answer 10

14 s

Question 11

Calculate the concentration of a sucrose solution that had an original concentration of 5.00 g / L after 6.00 hours and 20.0 minutes. The rate constant for this reaction at 300 K is 4.10 × 10−2 hr−1.

Answer 11

3.86 g / L

Question 12

Compound XY decomposes to form X and Y in a reaction that is first order with respect to XY and first order overall. The half-life for the reaction is 15.4s. What is the specific rate constant of this reaction as 25 degrees C?
XY -> X + Y

Answer 12

4.50 × 10−2 s−1

Question 13

If the temperature of the reactants is increased by 30° C, and all other factors remain constant, how will this affect the reaction rate?

Answer 13

It will increase 8 fold

Question 14

Consider the relationship among activation energy, temperature, and the specific rate constant of a reaction:
k = A

If Ea decreases, the effect will be all of the following except:

Answer 14

The reaction slows down.

Question 15

In the formula for the rate of a chemical reaction, which expression changes with temperature?

rate = k[A]m[B]n

Answer 15

k

Question 16

Which of the following is the Arrhenius equation for reaction rate?

Answer 16

k = Ae ^−Ea/RT

Question 17

Which of the following is not a constant in the Arrhenius equation?

Answer 17

T

Question 18

Given the following information, find the activation energy for the decomposition of acetaldehyde.

k1 = 1.05 × 10−3 M −1/2s−1 at 759 K
k2 = 2.14 × 10−2 M −1/2s−1 at 836 K

Answer 18

2.06 × 10^5 J / mol

Question 19

The molecularity of an elementary step of a reaction refers to:

Answer 19

the number of molecules that collide in the elementary step of a reaction.

Question 20

What is the molecularity of each step in the following reaction sequence? Step 1a: Cl2 → 2Cl
Step 1b: 2Cl → Cl2
Step 2: Cl + CHCl3 → HCl + CCl3
Step 3: Cl + CCl3 → CCl3

Answer 20

Step 1a: Unimolecular, Step 1b: Bimolecular, Step 2: Bimolecular, Step 3: Bimolecular

Question 21

Which of the following is the rate law expression for the following chemical reaction? This reaction occurs in one step and has no reaction intermediates.

2 NO(g) + O2(g) → 2 NO2(g)

Answer 21

k[ NO]2 [O2 ]

Question 22

In the formula for the rate of a chemical reaction, which expression changes with temperature?

rate = k[A]m [B]n

Answer 22

k

Question 23

In a proposed two-step mechanism for the reaction, CO(g) + NO2(g) → CO2(g) + NO(g), the second, fast, step is NO3 + CO → NO2 + CO2. What is the expected rate law of this reaction?

Answer 23

rate of reaction = k[ NO2 ]2

Question 24

The rate law for the reaction, 2NO(g) + O2(g) → 2NO2(g), is found to be: rate of reaction = k [ NO]2 [O2 ]2.

The first, fast step is 2NO(g) ↔ N2O2(g).

What is the value of Δ[ N2O2 ] / Δt ?

Answer 24

0

Question 25

A catalyst has which of the following properties?

Answer 25

A catalyst increases the rate of a reaction.