# Equilibrium Practice Test # 2

1.         The slowest of the following reactions is:

A.        Ag+(aq)   +  Cl-(aq)    AgCl(s)

B.         H+(aq)  +  OH-(aq)    2H2O(l)

C.        3Ba2+(aq)  +  2PO43-(aq)    Ba3(PO4)2(aq)

D.        Cu(s)  +  2Ag+(aq)    Cu2+(aq)  +  2Ag(s)

2.         The rate of a chemical reaction is equal to the slope of the line with axes labelled

x-axis                           y-axis

A.        time                              rate

B.         mass                             time

C.        volume of gas               time

D.        time                             concentration

3.         Consider the following reaction:  CH4(g)  +  2O2(g)    CO2(g)  +  2H2O(g)  +  heat

The diagram that represents the relationship between rate and temperature is: <

4.         Which of the following describes the energy of colliding particles as reacting molecules approach each other?

KE                               PE

A.                    decreases                   increases

B.                     increases                      decreases

C.                    decreases                     remains constant

D.                    remains constant           increases

5.         The average kinetic energy per molecule can be increased by

B.         increasing pressure

C.        increasing temperature

D.        increasing reactant concentration

6.         Consider the following reaction:  C(s)  +  2H2(g)    CH4(g)          ΔH  =  -74.8 kJ

Which of the following will cause an increase in the value of the Keq?

A.        increasing [H2]

B.         decreasing the volume

C.        finely powdering the C(s)

D.        decreasing the temperature

7.         Consider the following equilibrium:  H2(g)  +  I2(g)    2HI(g)

At equilibrium [H2]  =  0.00220 M, [I2]  =  0.00220 M, and [HI]  =  0.0156 M

The value of the Keq is

A.        3.10  x  10-4

B.         1.99  x  10-2

C.        5.03  x  101

D.        3.22  x  103

8.         Consider the rate diagram for the following reaction:  2HI(g)    H2(g)  +  I2(g) Which of the following occurs at t1?

D.        a decrease in volume

9.         Chemical equilibrium is said to be dynamic because

A.        the reaction proceeds quickly

B.         the mass of the reactants is decreasing

C.        the macroscopic properties are constant

D.        both forward and reverse rates are occurring

10.       Which equation has the largest value of Keq?

A.        N2(g)  +  O2(g)    2NO(g)                                              ΔH  =  21 kJ

B.         C2H6(g)    2C(s)  +  3H2(g)                                           ΔH  +  83 kJ

C.        H2(g)  +  1/2O2(g)    H2O(g)                                          ΔH  =  -240 kJ

D.        Ca(s)  +  3H2O(l)    Ca(OH)2(aq)  +  H2(g)                     ΔH  =  -240 kJ

11.       The value of the Keq can be changed by

## B.changing the temperature

C.        changing the reactant concentration

D.        changing the volume of the container

12.       Consider the following equilibrium:  PCl3(g)  +  Cl2(g)    PCl5(g)

When 0.40 mole of PCl3 and 0.40 mole of Cl2 are placed in a 1.00 L container and allowed to reach equilibrium, 0.244 mole of PCl5 are present. From this information, the value of the Keq is

A,        0.10

B.         0.30

C.        3.3

D.        10

13.       Consider the following equilibrium: PCl3(g)  +  Cl2(g)    PCl5(g)        Keq =  2.30

A 1.0 L container is filled with 0.05 mole PCl5, 1.0 mole PCl3, and 1.0 mole Cl2. The system proceeds to the

A.        left because the Trial Keq  >  Keq

B.         left because the Trial Keq  <  Keq

C.        right because the Trial Keq  >  Keq

D.        right because the Trial Keq  <  Keq

14.       Given the following system: 2CrO42-(aq)  +  2H+(aq)    Cr2O72-(aq)  +  H2O(l)

Which of the following chemicals, when added to the above system at equilibrium, would result in a decrease in [Cr2O72-]?

### A.NaOH

B.         HNO3

C.        Na2CrO4

D.        Na2Cr2O7

15.       What is the Keq expression for the following equilibrium?

3Fe(s)  +  4H2O(g)    Fe3O4(s)  +  4H2(g)

A.        Keq  =  [H2]4

B.         Keq  =   [H2]

[H2O]

C.        Keq  =  [H2]4

[H2O]4

D.        Keq  =  [Fe2O3][H2]4

[Fe][H2O]4

16.       Consider the following equilibrium: 2O3(g)    3O2(g)      Keq  =  65

Initially 0.10 mole of O3 and 0.10 mole of O2 are placed in a 1.0 L container, Which of the following describes the changes in concentrations as the reaction proceeds towards equilibrium?

[O3]                             [O2]

A.        decreases                     decreases

### B.decreasesincreases

C.        increases                      decreases

D.        increases                      increases

17.       Consider the following equilibrium: 2CrO42-(aq) +  2H+(aq)    Cr2O72-(aq)  +  H2O(l)

yellow                             orange

An unknown solution is added to an orange equilibrium system until the sample turns yellow. The solution could be

A.        KNO3

### B.NaOH

C.        NH4NO3

D.        CH3COOH

18.       Consider the following equilibrium:

CH3COOH(aq)    CH3COO-(aq)  +  H+(aq)  + heat

A stress was applied at time t1 and the data plotted on the following graph:

The stress imposed at time t1 is the result of B.         decreasing the temperature

D.        increasing the volume of the container

19.       Consider the following potential energy diagram for an equilibrium system: When the temperature of the system is increased, the equilibrium shifts to the

A.        left and the Keq increases

B.        left and the Keq decreases

C.        right and the Keq increases

D.        right and the Keq decreases

20.       Addition of a catalyst to an equilibrium system

A.        increases the value of the Keq

B.         increases the yield of the product

C.        has no effect on the rates of the reaction

### D.increases the rates of formation of both reactants and products

21.       Ammonia, NH3, is produced by the following reaction:

N2(g)   +  3H2(g)  D        2NH3(g)  +  energy

Which of the following would result in the highest concentration of ammonia at equilibrium?

A.        increasing the temperature and increasing the pressure

### B. decreasing the temperature and increasing the pressure

C.        increasing the temperature and decreasing the pressure

D.        decreasing the temperature and decreasing the pressure

22.       Consider the following equilibrium:

2NO2(g)  D  N2O4(g)                        Keq = 1.15

The equilibrium concentration of NO2 is 0.05 mol/L.  Calculate the equilibrium concentration of N2O4(g).

A.        0.22 mol/L

### B.0.29 mol/L

C.        0.43 mol/L

D.        0.58 mol/L

23.       Consider the following equilibrium:

H2(g) + I2 D 2HI(g)                       Keq = 50.0

What is the value Keq for the reaction rewritten as:

2HI(g)  D  H2(g)   +  I2(g) Keq = ?

A.        -50.0

### B.0.0200

C.        25.0

D.        50.0

24.       Consider the following equilibrium: 2NOCl(g)  D  2NO(g)  +  Cl2(g)

A flask is filled with NOCl, NO, and Cl2(g). Initially there were a total of 5.0 moles of gases present. When equilibrium is reached, there are a total of 8.0 moles of gases present. Which of the following explains the observation?

A.        The reaction shifted left because the Trial Keq > Keq

B.         The reaction shifted left because the Trial Keq < Keq

C.        The reaction shifted right because the Trial Keq > Keq

### D.The reaction shifted right because the Trial Keq < Keq

25.       Consider the following equilibrium:

4NH3(g)  +  5O2(g)  D  4NO(g)  +  6H2O(g)  +  energy

Which of the following will cause the equilibrium to shift to the left?

B.         removing some NO(g)

C.        increasing the volume

D.        decreasing the temperature

26.       A catalyst is added to a system already at equilibrium. How are the forward and reverse reaction rates affected by the addition of the catalyst.

Forward Rate               Reverse Rate

A.        increases                    increases

B.         increases                      constant

C.        constant                        decreases

D.        constant                        constant

27.       Consider the following equilibrium: 2NOBr(g)  D  2NO(g)  +  Br2(g)  Keq  =  0.064

At equilibrium, a 1.00 L flask contains 0.030 mole NOBr and 0.030 mole NO. How many moles of Br2 are present?

A.        0.0019

B.        0.064

C.        0.030

D.        0.47

28.       Which of the following does not apply to all chemical equilibrium systems?

A.        They are closed.

B.         The macroscopic properties are constant

C.        Forward and reverse rates are equal

D.        There are equal concentrations of reactants and products

29.       The relationship between Ea and reaction rate is best represented as 30.       The relationship between Keq and temperature for an exothermic reaction is best represented as 31.       The relationship between reaction rate and temperature is best represented by 32.       The relationship between Ea and temperature is best represented by 32.       Methanol, CH3OH, can be produced by the following:

CO(g)  +  2H2(g)  D  CH3OH(g)  +  energy

The conditions necessary to maximize the equilibrium yield of CH3OH are

A.        low temperature and low pressure

B.         high temperature and low pressure

C.        low temperature and high pressure

D.        high temperature and high pressure

33.       Consider the following equilibrium:  2NO(g)  +  O2(g)  D  2NO2(g)  +  energy

When the volume of the container is increased, the equilibrium shifts to the

A.        left and the Keq decreases

B.         right and the Keq increases

C.        left and the Keq remains constant

D.        right and the Keq remains comstant

34.       Consider the following reaction:

C3H8(g)  +  5O2(g)  Š  3CO2(g)  +  4H2O(g)                            @H  =  -2202 kJ

Which of the following applies to the forward reaction?

Entropy                        Enthalpy

A.        increases                      increases

#### B.increasesdecreases

C.        decreases                     increases

D.        decreases                     decreases

# Subjective

1.         Consider the following equilibrium:

N2H4(g)  +  2O2(g)  D  2NO2(g)  +  2H2O(g)

More oxygen is added to the above equilibrium. After the system re-establishes equilibrium, identify the substance(s), if any, that have a net

a)         increase in concentration           NO      H2O     O2

b)         decrease in concentration          N2H4

2.         Given the following equilibrium: H2(g)  +  I2(g)        D  2HI(g)

Initially, 0.200 mole H2 and 0.200 mole I2 were placed into a 1.0 L container. At equilibrium, the [I2] is 0.040 M. Calculate the Keq.

H2(g)     +          I2(g)             D                          2HI(g)

I           0.200 M          0.200 M                      0

C         0.160 M          0.160 M                      0.320 M

##### E0.040 M0.040 M0.320 M

Keq     =          (0.320)2           =          64

(040)2

3.         Consider the following equilibrium: 2CrO42-(aq) +  2H+(aq)    Cr2O72-(aq)  +  H2O(l)

yellow                             orange

When HCl is added, the solution turns orange. Explain why this colour change occurs.

Adding HCl increases the [H+] and shifts the system right turning orange.

4.         Consider the following equilibrium system:

N2(g)   +  3H2(g)  D        2NH3(g)  +  energy

A 1.00 L container is filled with 7.0 mole NH3 and the system proceeds to equilibrium as indicated by the graph. a)         Draw and label the graph for N2 and H2. Fill in an ICE chart if you are not sure how to do this.

N2(g)     +          3H2(g)      D      2NH3(g)

I           0                      0                      7.0

C         3.0                   9.0                   6.0

E          3.0                   9.0                   1.0

b)         Calculate the Keq for the above reaction.

Keq     =          (1.0)2   =          0.00046

(3.0)(9.0)3

5.         Consider the following equilibrium 2NO(g)  +  O2(g)  D  2NO2(g)             Keq  =  1.5

0.800 mole NO, 0.600 moles O2, and 0.400 moles NO2 are placed in a vessel that 2.0 L. Show by calculation that the reaction is not at equilibrium? What will happen to [O2] as equilibrium is approached?

Trial Keq        =                      (0.200)2           =          0.833   <    Keq  =  1.5

(0.400)2(0.300)

Not at equilibrium                  Shifts Right                [O2] will decrease.

6.         Consider the following equilibrium:

SO3(g)  +  NO(g)  D  NO2(g)  +  SO2(g)               Keq  =  0.500

Exactly 0.100 mole SO3 and 0.100 mole NO were placed in a 1.00 L flask and allowed to go to equilibrium. Calculate the equilibrium concentration of SO2.

SO3(g)    +          NO(g)  D        NO2(g)     +       SO2(g)

I           0.100               0.100               0                      0

C         x                      x                      x                      x

E          0.100 – x         0.100 – x         x                      x

x2                     =          0.500

(0.100 – x)2

x                      =          0.7071

0.100 – x

1.7071x  =  0.07071

x  =  0.0414 M

[SO2]  = 0.0414 M