Quiz # 3           Yield/Graphing/LeChatelier’s Principle                    Answers

1.         When a catalyst is added to an equilibrium system, the forward reaction

A.        Increases and the reverse decreases

B.         Decreases and the reverse decreases

C.        Decreases and the reverse increases

D.        Increases and the reverse increases

2.         Consider the following concentration versus time graph for the equilibrium

N2O4(g)                   2NO2(g) t        TIME(S)

At time= “t”, which one of the following stresses occurred

B.         Pressure was changed

C.        Temperature was changed

D.        Concentration of NO2 was changed

3.         Which of the following reactions will shift left when pressure is increased and when temperature is decreased?

A.        N2(g)  +  2O2(g)  + heat          2NO2(g)

B.         N2(g)  +  3H2(g)               2NH3(g)  + heat

C.        CH4(g)  +  H2O(g)  + heat                 CO(g)  +  3H2(g)

D.        CS2(g)  +  4H2(g)                CH4(g)  +  2H2S(g)  +  heat

4.         Consider the following graph, which relates to this equilibrium

N2(g)  +  3H2(g)                   2NH3(g)                    ∆H = -92kJ Which of the following caused the changes in the concentrations at time t ?

B.         Removal of H2

C.        Decrease in temperature

D.        Decrease in reaction volume

5.       Consider the following equilibrium: CH4(g)  +  H2O(g)  +  heat       CO(g)  +  3H2(g)

In which of the following will both stresses shift the equilibrium right

A.        A decrease in temperature and a decrease in volume

B.         An increase in temperature and a decrease in volume

C.        A decrease in temperature and an increase in volume

D.        An increase in temperature and an increase in volume

6.       Consider the following equilibrium system: N2(g) + 3H2(g)          2NH3(g)  +  92 kJ

In order to maximize the yield for this reaction, the best conditions are:

A. Low pressure and low temperature

B. Low pressure and high temperature

C. High temperature and low pressure

D. High pressure and low temperature

7.       Consider the following equilibrium system: NH3(aq) + H2O(l)   NH+4(aq) + OH--(aq)

Which of the following when added to the above equilibrium system would cause an increase in [ OH-]

A. NH3

B. H2O

C. NH4+

D. HCl

8.         Consider the following reversible reaction:  Fe3+(aq)  +  SCN-(aq)        FeSCN2+(aq)

A solution of Fe(NO3)3 is added to a solution of KSCN. Which one of the following statements

describes the changes in forward and reverse reaction rates as the reaction moves towards equilibrium?

A.        Forward and reverse rates increase

B.         Forward and reverse rates decrease

C.        Forward rate increases and reverse rate decrease

D.        Forward rate decreases and reverse rate increase

9.         Consider the following equilibrium:  N2(g)  +  O2(g)      2NO(g)      ∆H= + 181 kJ

When the temperature is decreased, the equilibrium

A. Shifts left and [NO] decreases

B. Shifts left and [NO] increases

C. Shifts right and [NO] increases

D. Shifts right and [NO] decreases

10.       Consider the following equilibrium: N2(g)  +  3H2(g)           2NH3(g)  +  92 kJ

In which of the following will both changes shift the equilibrium right?

A. An increase in volume and a decrease in temperature

B. An increase in volume and a increase in temperature

C. A decrease in volume and a decrease in temperature

D. A decrease in volume and an increase in temperature

11.       Consider the following equilibrium: CaCO3(s)  +   556 kJ      CaCO(s)  +  CO2(g)

The equilibrium will shift to the right

C. The temperature is increased

D. The temperature is decreased

12.       Consider the following equilibrium: SO2(g)  +  NO2(g)    SO3(g)  +  NO(g)  + energy

The equilibrium does not shift with a change in the

A. Volume

B. Temperature

C. Concentration of products

D. Concentration of reactants

13.       Consider the following equilibrium:  2Hl(g)               H2(g)   +  I2(g)

At constant temperature and volume, more I2 is added to the above equilibrium.

A new state of equilibrium results from a shift to the

A. Left with a net decrease in [H2]

B. Left with a net increase in [H2]

C. Right with a net increase in [H2]

D. Right with a net decrease in [H2]

14.       Consider the following diagram for the equilibrium system:

Energy   +    N2O4(g)                   2NO2(g) A.        [NO2] was increased.

B.         [N2O4] was decreased.

C.        Temperature was increased.

D.        Temperature was decreased.

15.       Consider the following diagram for the equilibrium system:

Energy   +    N2O4(g)                   2NO2(g) A.        [NO2] was increased.

B.         [N2O4] was decreased.

C.        Temperature was increased.

D.        Temperature was decreased.

16.       Consider the following diagram for the equilibrium system:

Energy   +    N2O4(g)                   2NO2(g) A.        [NO2] was increased.

B.         [N2O4] was decreased.

C.        Temperature was increased.

D.        The Volume was decreased.

17.       Which of the following describes the temperature and pressure needed for

the maximum yield of NO2?

Energy   +    N2O4(g)                   2NO2(g)

Temperature                 Pressure

A.        low                               low

B.         low                               high

C.        high                             low

D.        high                              high

18.       Which of the following describes the temperature and pressure needed for

the maximum yield of NH3?

N2(g)  +  3H2(g)           2NH3(g)  +  92 kJ

Temperature                 Pressure

A.        low                               low

B.        low                               high

C.        high                              low

D.        high                              high

19.       Which of the following describes the temperature and pressure needed for

the maximum yield of CO2?

CaCO3(s)       CaCO(s)  +  CO2(g)        ΔH  =  +215 kJ

Temperature                 Pressure

A.        low                               low

B.         low                               high

C.        high                             low

D.        high                              high

20.       Consider the following equilibrium: CaCO3(s) CaO(s)  + CO2(g)  ΔH = +160 kJ

Which starting materials could establish an equilibrium?

1          CaCO3(s)                      2          CaO(s)

3          CaO(s)   and CO2(g)       4          CaCO3(s) and CO2(g)

A.        1, 2, 3 only

B.         1, 2, 4 only

C.        1, 3, 4 only

D.        3, 4 only

Consider the following reaction for the next five questions 21 to 25.

4NH3(g)   +  3O2(g)    2N2(g)  +  6H2O(l)   +  1250 kJ

21.       Which of the following would cause the concentration of NH3 at equilibrium to increase?

A.        an increase in [O2]

B.        a increase in volume

C.        a decrease in temperature

D.        an increase in temperature

22.       What happens when NH3 is added to the above system?

Equilibrium                               [N2]

A.        no shift                          unchanged

B.        shifts right                     decreases

C.        shifts right                   increases

D.        shifts left                       increases

23.       If some O2 is removed from the system, what happens to the forward and

reverse reaction rates after equilibrium is re-established?

Forward Reaction Rate Reverse Reaction Rate

A.        increases                                  decreases

B.        decreases                                decreases

C.        increases                                  increases

D.        decreases                                 increases

24.       If some O2 is injected into the system, what happens to the forward and

reverse reaction rates during the shift to re-establish equilibrium?

Forward Reaction Rate Reverse Reaction Rate

A.        increases                                  decreases

B.        decreases                                 decreases

C.        increases                                  increases

D.        decreases                                increases

25.       Consider the equilibrium: N2(g)  +  3H2(g)           2NH3(g)  +  92 kJ

The following diagram represents the rate of the reverse reaction.

 t1 Which of the following stresses explains what happened at t1 ?

A.        [H2] increased.

B.         [N2] decreased.

C.        [NH3] increased.

D.        [NH3] decreased.

26.       Consider the equilibrium: N2(g)  +  3H2(g)           2NH3(g)  +  92 kJ

The following diagram represents the rate of the forward reaction.

 t1 Which of the following stresses explains what happened at t1 ?

A.        [H2] increased.

B.         temperature was lowered

C.        [NH3] increased.

D.        [NH3] decreased.

27.       Consider the equilibrium: N2(g)  +  3H2(g)           2NH3(g)  +  92 kJ

The following diagram represents the rate of the reverse reaction.

 t1 Which of the following stresses explains what happened at t1 ?

A.        [H2] increased.

B.         [N2] decreased.

C.        [NH3] increased.

D.        [NH3] decreased.

28.       A small amount of NaOH is added to the following equilibrium system:

2CrO42-   +   2H+         Cr2O72-(aq)      +   H2O(l)

How do the [CrO42-] and the reverse reaction rate change as equilibrium is re-established?

[CrO42-]           Reverse Rate

A.        increases          increases

B.        increases        decreases

C.        decreases         decreases

D.        decreases         increases

29.       A small amount of H2SO4 is added to the following equilibrium system:

2CrO42-   +   2H+         Cr2O72-(aq)      +   H2O(l)

How do the [CrO42-] and the reverse reaction rate change as equilibrium is re-established?

[CrO42-]           Reverse Rate

A.        increases          increases

B.         increases          decreases

C.        decreases         decreases

D.        decreases       increases

30.       A small amount of NaOH is added to the following equilibrium system:

2CrO42-   +   2H+         Cr2O72-(aq)      +   H2O(l)

How do the [Cr2O72-] and the reverse reaction rate change as equilibrium is re-established?

[Cr2O72-]          Reverse Rate

A.        increases            increases

B.         increases          decreases

C.        decreases         decreases

D.        decreases         increases

31.       A small amount of H2SO4 is added to the following equilibrium system:

2CrO42-   +   2H+         Cr2O72-(aq)      +   H2O(l)

How do the [Cr2O72-] and the reverse reaction rate change as equilibrium is re-established?

[Cr2O72-]          Reverse Rate

A.        increases        increases

B.         increases          decreases

C.        decreases         decreases

D.        decreases         increases