Exam 2

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Question #1

Among the following binary halogen acids
HF, HCl, HBr, HI,
the formula that represents the strongest acid is =

A HBr

B HF

C HCl

D HI

Question #2

According to Brønsted and Lowry, which one of the following is not a conjugate acid-base pair?

A HI/I-

B CH3OH2+/CH3OH

C H2/H-

D HSO4-/SO42-

E H3O+/OH-

Question #3

Consider the following reaction at equilibrium:
2SO2 (g) + O2 (g) <--> 2SO3 (g) ΔH° = -99 kJ

Le Châtelier’s principle predicts that a(n) decrease in temperature will result in ________.

A a decrease in the partial pressure of SO2, a decrease in the partial pressure of O2

B an increase in the partial pressure of O2, a decrease in Keq

C no changes in equilibrium partial pressures

Question #4

For the reaction of nitrogen and oxygen to form nitrogen dioxide,
N2(g) + 2O2(g) ⇌ 2NO2(g) Kc = 4.0×103

If the reaction mixture is found to contain 2.0 M NO2 and 0.10 M N2 and 0.10 M O2, what is the value of Q and what does this mean?

A Q = 2×102 and the reaction will proceed towards the reactants

B Q = 2×102 and the reaction will proceed towards the products

C Q = 4×103 and the reaction will proceed towards the reactants

D None of the choices are correct

E Q = 4×103 and the reaction will proceed towards the products

Question #5

For a chemical reaction at equilibrium, which of the following will not change the value of the equilibrium constant K?
I. Changing the temperature
II. Changing the total concentration of reactants or products
III. Changing the total volume

A I and II only

B III only

C II only

D II and III only

E I only

Question #6

Which change in the system will not affect the equilibrium in the reaction below?
N2O5(g) ⇌ NO2(g) + NO3(g)

A increase the total pressure

B None of the choices

C increase the volume

D increase the partial pressure of NO2(g) and increase the volume

E decrease the amount of NO3

F adding water

Question #7

Based on Le Châtelier’s principle, increasing volume at constant temperature in the following reaction will decrease the concentrations of reactants.

A 2N2 (g) + O2 (g) ⇌ 2N2O (g)

B N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

C N2 (g) + O2 (g) ⇌ 2NO (g)

D N2 (g) + 2O2 (g) ⇌ 2NO2 (g)

E N2O4 (g) ⇌ 2NO2 (g)

Question #8

Consider the equilibrium: 2ICl(g) ⇄ I2 (g) + Cl2 (g) Kc= 15.0
If initially z moles of ICl, 1mole of I2 and 2 moles of Cl2 were placed in a 1.0 L container at 10 oC and as equilibrium is reached concentration of I2 decreases by 20%, calculate the number of moles ICl initially present.

A 2.99

B 3.39

C None of the choices are correct

D 2.3

E 4.25

Question #9

When a certain compound A is heated it decomposes according to the following reaction:

2 A(s) ⇌ B(s) + 2C(g) + D(g)

If sufficient Solid A is placed in a container and heated to 90°C, the total pressure of the gases is 2.00 atm. What is the value of Kp at that temperature?

A 32

B 1.19

C 0.791

D 0.25

E 0.5

F None of the choices are correct

Question #10

Given the following hypothetical reactions with K1 and K2 values :
1). 1 A (g) + 1/2 B(s) ⇌ 1D (aq) K1 = 5
2). 2 C(g) + 2 D (aq) ⇌ 4A(g) + 2 B(s) K2 = 2

What is value of the equilibrium constant that will result from the above reactions:

3). 4 A(g) + 2B ⇌ C(g) + 3D (aq) K3 = ?

A 100

B 17.7

C None of the choices are correct

D 35.4

E 6.25

Question #11

The rate at which popcorn pops was measured at two different temperatures. How many times faster does the popcorn pop at 250°C compared with that at 210°C when the activation energy is 53.8 kJ/mol?

A 125

B 12.7

C 140

D 3.9

E 2.8

Question #12

The following reaction of [A] has a rate constant of 0.0250 M s-1:
A → B
If in 33 seconds the A reacts by 70.0%. What would be the half life ? .

A 14.1s

B 33.9s

C None of the choices are correct

D 26s

E 23.6s

F 10.4s

Question #13

The rate of a reaction is found to double when the concentration of one reactant is quadrupled. The order of the reaction with respect to this reactant is ________

A 2

B 1

C 0

D 1/2

E -2

F -1

Question #14

After 55 years, what mass (in g) remains of a 200.0 g sample of a radioactive isotope with a half-life of 10.0 years?

A 4.4 g

B 170 g

C 0.22 g

D 51 g

Question #15

The initial rate data for the reaction 2N2O5(g) <--> 4NO2(g) + O2(g) is shown in the following table.
Experiment [N2O5] (M) Rate (M/s)
1) 2.56 x 103 450
2) 1.28 x 102 22.5
What would be units for k

A 1/s2

B 1/s

C 1/s3

D 1/M

Question #16

The initial rate data for the reaction 2N2O5(g) <--> 4NO2(g) + O2(g) is shown in the following table.
Experiment [N2O5] (M) Rate (M/s)
1) 2.56 x 103 450
2) 1.28 x 102 22.5
Determine the value of the rate constant for this reaction k =

A 1.01

B 0.931

C 0.176

D 0.518

Question #17

The reaction is run at two temperatures where temperature 1 is higher than temperature 2. Which relationship is correct for either rate constant (k1 or k2) or activation energy (Ea,1 and Ea,2)?

A k1 < k2

B Ea,1 < Ea,2

C k1 > k2

D Ea,1 > Ea,2

Question #18

Nitric oxide and nitrogen dioxide are found in photochemical smog. Nitrogen dioxide is formed from nitrogen monoxide in the exhaust of automobile engines. A possible mechanism for this reaction is given below, where equilibrium is quickly established in steps 1 and 2. What is the rate law predicted by this mechanism? (you may keep the k general)
Overall Reaction: 2NO(g) + O2(g) → 2NO2(g)
Mechanism:
Step 1 (fast, equilibrium): NO + NO ↔ N2O2
Step 2 (fast, equilibrium): N2O2 ↔ N + NO2
Step 3 (slow): N + O2 → NO2

A Rate = [NO2]2 / ([NO]2[O2])

B Rate = k[NO][O2]

C Rate = k [NO]2[O2] / [NO2]

D Rate = k[NO]2[O2]

E Rate = k[NO]2

Question #19

The reaction of

2N2O5(g) → 4NO2(g) + O2(g)

is experimentally determined to be zero order. What experimental data would support this conclusion?
I . Plotting 1 / [N2O5] vs. time would be linear
II. The half-life is independent of the initial concentration
III. Doubling the initial concentration of N2O5 would have no effect on the initial rate.

A Only III.

B Only II.

C I. and III.

D None of the choices are correct

E II. and III.

Question #20

Given the following Mechanism:
Step 1: H2O2(aq) + I–(aq) → H2O(l) + OI–(aq) (slow)
Step 2: H2O2(aq) + OI–(aq) → H2O(l) + O2(g) + I–(aq) (fast)
Identify the catalyst in the reaction

A I–

B H2O

C O2

D OI–

E H2O2

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