Question

 

(1) The activation energy, E_a, is the energy difference between the reactants and the products in a chemical reaction.
(2) The activation energy is the energy barrier that must be overcome by reactants for a reaction to occur.
(3) The frequency factor, A, in the Arrhenius equation relates to the number of collisions and the fraction of those collisions that have the proper geometry for a reaction to occur.

A.2 only

B.1 only

C.2 and 3

D.1 and 2

E.1 and 3

2.For a hypothetical reaction the rate constants are 3.11×10^-5 s^-1 at 25 °C and 1.20×10^-3 s^-1 at 40.0 °C. From these data, calculate the activation energy for this reaction.

A.189 kJ/mol

B.-1.89×10⁵ kJ/mol

C.-189 kJ/mol

D.2.02×10³ kJ/mol

3.The activation energy, E_a, is 139.7 kJ mol^-1 for the following gas-phase reaction:

HI + CH₃I  CH₄ + 2 I₂

Calculate the fraction of molecules whose collisions would be energetic enough to react at 270 °C.

A.3.64×10^-14

B.0.970

C.0.940

D.4.36×10^-2

4.Select all that apply.

The transition state:

A.is easily achieved in most reactions.

B.requires more energy to achieve in a catalyzed reaction.

C.represents the state at which the reactants have the least free energy.

D.is the state of reactants which have the necessary energy and the correct arrangement of atoms to produce products.

E.is at the top of the curve in an activation energy profile.

5.Choose the statement that is not correct for catalysts.

. A.The concentration of the catalyst may appear in the rate law.

B.A catalyst increases the reaction rate.

C.A catalyst changes the mechanism of the reaction.

D.A catalyst changes the amount of heat that the reaction can evolve.

6.You purchase a glow stick during an evening parade. After it ends, your roommate tells you that if you place it in the freezer, it will glow for a longer time. Assuming she knows what she is talking about, why would this be true?

A. Your roommate simply made up the story to annoy you.

B.Reaction rates can be expected to decrease as temperature is reduced.

C.It's dark in a closed freezer, preventing the stick from glowing.

D.There is less oxygen inside the freezer than outside, so the reaction slows down.

7.Which of the following statements correctly describes a chemical system that has reached equilibrium?

(1) The forward rate of reaction is greater than the reverse rate of reaction.
(2) No further macroscopic changes in the system are observed.
(3) The concentrations of reactants and products must be equal.

A.2 only

B.1 only

C.1 and 2

D.1, 2, and 3

E.3 only

8.For the following reaction,

N₂(g) + 3 H₂(g)  2 NH₃(g) K_p = 4.5 × 10³

the partial pressures are as follows:

	partial pressure (atm)
N2	10
H2	5.0
NH3	5.0

9.Calculate Q and compare it to K_p. Will the system shift to the left or the right to achieve equilibrium, or is it at equilibrium?

A. Q = 50 shift left

B.Q = 4.5×10³ at equilibrium

C.Q = 2.0×10^-2 shift left

D.Q = 2.0×10^-2 shift right

10.What is the chemical reaction that is described by the equilibrium constant expression below?

	[ CN- ][ H3O+ ]
K =
	[ HCN ]

 

A.HCN (aq) + OH^- (aq)  CN^- (aq) + H₂O (l)

B.CN^- (aq) + H₃O⁺ (aq)  HCN (aq) + H₂O (l)

C.CN^- (aq) + OH^- (aq)  HCN (aq) + H₂O (l)

D.HCN (aq) + H₂O (l)  CN^- (aq) + H₃O⁺ (aq)

E.CN^- (aq) + H₃O⁺ (aq)  HCN (aq)

11.Choose the correct equilibrium expression for this reaction:

CH₄(g) + H₂O(g)  CO(g) + 3 H₂(g)

A.

	[H2O][H2]
Kc =
	[CH4][CO]

 

B.

	[CO][H2]3
Kc =
	[CH4][H2O]

 

C.

	[CH4][H2O]
Kc =
	[CO][3 H2]

 

D.

	[CO][H2]
Kc =
	[CH4][H2O]

12.The reaction: 2 NOCl(g)  2 NO(g) + Cl₂(g)

is studied at a certain temperature. Initially, 0.100 mol NOCl is placed in an empty 1.0-L flask. At equilibrium, the concentration of Cl₂ is 0.020 M. Calculate K_c for the reaction.

A.75

B.1.3×10^-2

C.110

D.8.9×10^-3

E.0.22

13.BrCl is put into an empty 1.00 L container. At equilibrium, the molar concentration of BrCl is 0.382, and that of Br₂ is 0.319. Evaluate the equilibrium constant for the following reaction.

Br₂(g) + Cl₂(g)  2BrCl(g)

A.5.74

B.0.457

C.0.699

D.1.43

14.The equilibrium constant for the dissolution of AgI(s) in water is 1.5×10^-16.

AgI(s)  Ag ⁺(aq) + I^-(aq)

A solution is prepared by diluting 2.0 mol AgI, 1.2×10^-7 mol Ag⁺, and 3.0×10^-7 mol I^- to a volume of 1.0 L. Calculate the reaction quotient and determine whether a reaction occurs.

A.Q < K; Ag⁺ and I^- combine to form AgI(s) until equilibrium is established.

B.Q > K; AgI(s) dissolves until equilibrium is established.

C.Q > K; Ag⁺ and I^- combine to form AgI(s) until equilibrium is established.

D.Q < K; AgI(s) dissolves until equilibrium is established.

E.Q = K; no reaction occurs.

15.The effect of increasing the temperature of an endothermic reaction is the same as:

A.Q > K

B.Q = K

C.removing reactants

D.Q < K

E.adding products

16.For the following reaction,

NO(g) + Br₂(g)NOBr₂(g)

what effect would increasing the volume have on the system?

A.The equilibrium would go to completion

B.The equilibrium would remain the same

C.The equilibrium would shift to the left

D.The equilibrium would shift to the right

17.This question refers to the equilibrium given below in which all reactants and products are gases.

CH₄ + H₂O  CH₃OH + H₂ + heat

Indicate the effect of the changing condition on the position of equilibrium.

Add CH₄ to the mixture.

A.Can shift to right or left

B.Shifts left

C.Shifts right

D.No effect

Answer 1

Answer:

C.2 and 3

2.For a hypothetical reaction the rate constants are 3.11×10^-5 s^-1 at 25 °C and 1.20×10^-3 s^-1 at 40.0 °C. From these data, calculate the activation energy for this reaction.

ln K2/K1 = -Ea/R (1/T1-1/T2)

ln(1.20×10^-3 / 3.11×10^-5) = -Ea / 8.314 (1/268 - 1 / 313)

3.653 = -Ea / 8.314 (1.682 X 10^-4)

Ea = -1.89 X 10⁵ J = -189kJ

A.189 kJ/mol

4.Select all that apply.

The transition state:

D.is the state of reactants which have the necessary energy and the correct arrangement of atoms to produce products.

E.is at the top of the curve in an activation energy profile.

5.Choose the statement that is not correct for catalysts.

. A.The concentration of the catalyst may appear in the rate law.

D.A catalyst changes the amount of heat that the reaction can evolve.

6.You purchase a glow stick during an evening parade. After it ends, your roommate tells you that if you place it in the freezer, it will glow for a longer time. Assuming she knows what she is talking about, why would this be true?

C.It's dark in a closed freezer, preventing the stick from glowing.

7.Which of the following statements correctly describes a chemical system that has reached equilibrium?

(2) No further macroscopic changes in the system are observed.
A.2 only

8.For the following reaction,

N₂(g) + 3 H₂(g)  2 NH₃(g) K_p = 4.5 × 10³

the partial pressures are as follows:

	partial pressure (atm)
N2	10
H2	5.0
NH3	5.0

9.Calculate Q and compare it to K_p. Will the system shift to the left or the right to achieve equilibrium, or is it at equilibrium?

Q = p²NH3 / p³H2 X pN2 = (5)² / (5)³(10) = 2.0×10^-2

Kp > Qp

D.Q = 2.0×10^-2 shift right

10.What is the chemical reaction that is described by the equilibrium constant expression below?

D.HCN (aq) + H₂O (l)  CN^- (aq) + H₃O⁺ (aq)

11.Choose the correct equilibrium expression for this reaction:

CH₄(g) + H₂O(g)  CO(g) + 3 H₂(g)

Kc = [CO][H₂]³ / [CH₄][H₂O]

12.The reaction: 2 NOCl(g) ---> 2 NO(g) + Cl₂(g)

is studied at a certain temperature. Initially, 0.100 mol NOCl is placed in an empty 1.0-L flask. At equilibrium, the concentration of Cl₂ is 0.020 M. Calculate K_c for the reaction.

Answer: Kc = [Cl2] [NO]² /[NOCl]²

two moles of NOCl will give one mole of Cl2

Let x moles of NOCl dissociates, they will give x/2 moles

x/2 = 0.02

x = 0.04

0.1-x = 0.06

Kc = (0.02) (0.04)² / (0.06)²

D.8.9×10^-3

13.BrCl is put into an empty 1.00 L container. At equilibrium, the molar concentration of BrCl is 0.382, and that of Br₂ is 0.319. Evaluate the equilibrium constant for the following reaction.

                 Br₂(g) + Cl₂(g) ---> 2BrCl(g)

Initial           0           0                a

Change       +x          +x               -2x

Equilbr      x            x                a-2x

Kc' = [Br2][Cl2] / [BrCl]² = x2 / (a-2x)²

Given that x = 0.319

a-2x = 0.382

a = 1.02

Kc' = 0.319² /0.382² = 0.697

Kc = 1 / Kc' = 1.433

D.1.43

14.The equilibrium constant for the dissolution of AgI(s) in water is 1.5×10^-16.

AgI(s)  Ag ⁺(aq) + I^-(aq)

A solution is prepared by diluting 2.0 mol AgI, 1.2×10^-7 mol Ag⁺, and 3.0×10^-7 mol I^- to a volume of 1.0 L. Calculate the reaction quotient and determine whether a reaction occurs.

Qc = [Ag⁺] [I^-] / [AgI]

Qc = 1.2×10^-7 * 3.0×10^-7 / 2

Qc = 1.8×10^-14

Qc > Kc

C.Q > K; Ag⁺ and I^- combine to form AgI(s) until equilibrium is established.

15.The effect of increasing the temperature of an endothermic reaction is the same as:

C.removing reactants

E.adding products

16.For the following reaction,

NO(g) + Br₂(g)   ---> NOBr₂(g)

what effect would increasing the volume have on the system?

C.The equilibrium would shift to the left

17.This question refers to the equilibrium given below in which all reactants and products are gases.

CH₄ + H₂O  CH₃OH + H₂ + heat

Indicate the effect of the changing condition on the position of equilibrium.

Add CH₄ to the mixture.

C.Shifts right