Equilibrium     Quiz #6            Enthalpy and Entropy                        Answers

1.         In which of the following reactions does the tendency towards minimum enthalpy and maximum entropy oppose each other?

A.        3O3(g)         2O2(g)                                           ΔH =  +285KJ

B.         1/2O2(g)    +    O2(g)      NO2(g)                         ΔH =  +34KJ

C.        2H2O(g)   2H2(g)    +   O2(g)                            ΔH =  +484KJ

D.        P4(s)    +   6H2(g)   4PH3(g)                               ΔH =  +37KJ

2.         In which of the following systems will the factors of entropy and enthalpy both favour the reactants.

A.        3C(s)   +   3H2(g)     +heat      C3H6(g)

B.         PCl5(g)    +    heat       PCl3(g)     +    Cl2(g)

C.        NH4Cl(s)    +   heat        NH4+(aq)   +    Cl-(aq)

D.        Cl2(g)     +   2HI(g)         I2(g)    +   2HI(g)   +   heat

3.         For an exothermic reaction at equilibrium, an increase in temperature will cause the equilibrium to shift

A.        left and the Keq increases

B.        left and the Keq decreases

C.        right and the Keq increases

D.        right and the Keq decreases

4.         Consider the following equilibrium: COCl2(g)  CO(g) + Cl2(g)     Keq  =   8.1 x  10-4

For the above system,

A.        [COCl2]  <   [CO][Cl2]

B.         [COCl2] = [CO][Cl2]

C.        [COCl2]> [CO][Cl2]

D.        [COCl2] = 1/[CO][Cl2]

5.         The value of the equilibrium constant will change when

A.        a catalyst is used

B.        temperature changes

C.        product concentrations change

D.        the volume of a gaseous system changes

6.         In an exothermic equilibrium reaction involving only gases, the value of the Keq can be decreased by

B.         removing some reactant gas

C.        increasing the temperature

D.        decreasing the temperature

7.         Consider the following:    H2(g)  + CO2(g)  CO(g) + H2O(g)     ΔH  =  +41KJ

The temperature of the above equilibrium system is increased while kept at a constant volume.

A new state of equilibrium is established in which there is

A.        an increase in [CO] and a decrease in Keq

B.        an increase in [CO] and a increase in Keq

C.        an increase in [CO2] and a decrease in Keq

D.        an increase in [CO2] and a increase in Keq

8.         Consider the following equilibrium: 2NO2(g)      N2O4(g)    +  59KJ

For the above reaction,

A.        both minimum enthalpy and maximum entropy favour the products.

B.         both minimum enthalpy and maximum entropy favour the reactants.

C.        minimum enthalpy favours reactants and maximum entropy favours products.

D.        minimum enthalpy favours products and maximum entropy favours reactants.

9.         In which of the following does entropy decrease?

A.        NaCl(s)    Na+(aq)   +    Cl-(aq)

B.        4NO(g)   +  6H2O(g)       4NH3(g)   +    5O2(g)

C.        2NaCHCO3(s)          Na2CO3(s)    +   CO2(g)   +   H2O(g)

D.        CaCO3(s)   +    HCl(aq)      CaCl2(aq)     +   CO2(g)      +  H2O(l)

10.       Consider the following possible reaction:  N2O(g)  +  NO2(g)     3NO(g)  + 120 KJ

Which of the following statements is correct?

A.        Minimum enthalpy and maximum entropy both favour the products.

B.         Minimum enthalpy and maximum entropy both favour the reactants.

C.        Minimum enthalpy favours the reactants and maximum entropy favours the products.

D.        Minimum enthalpy favours the products and maximum entropy favours the reactants.

11.       Consider the following equilibrium: COCl2(g)         CO(g)     +     Cl2(g)

At equilibrium in a 1.0L container, there are 3.0 mol COCl2, 0.49 mol CO, and 0.49 mol Cl2.

At constant temperature the volume of the above system is decreased to 0.50L. When equilibrium is reestablished the

A.        concentrations of all three gases have increased

B.         concentrations of all three gases have decreased

C.        [COCl2] has increased and [CO] and [Cl2] have decreased

D.        [COCl2] has decreased and [CO] and [Cl2] have increased

12.  Chemical systems move toward positions of

A.        minimum enthalpy and maximum entropy

B.         maximum enthalpy and minimum entropy

C.        constant enthalpy and constant entropy

D.        maximum enthalpy and maximum entropy

13.       Consider the equilibrium: H2(g)    2H(g)    Keq  =  1.2  x  10-71

The value of the equilibrium constant for the above system indicates that

A.        the reaction rate is very slow

B.         the equilibrium is exothermic

C.        reactants are favoured in this equilibrium

D.        a catalyst is necessary to establish equilibrium

14.       Consider the following reaction:

Na2CO3(s)   +    HCl(aq)      2NaCl(aq)     +   CO2(g)      +  H2O(l)           ΔH = -27.7 KJ

In this reaction,

A.        Minimum enthalpy and maximum entropy both favour the products.

B.         Minimum enthalpy and maximum entropy both favour the reactants.

C.        Minimum enthalpy favours the products and maximum entropy favours the reactants.

D.        Minimum enthalpy favours the reactants and maximum entropy favours the products.

15.       In an endothermic equilibrium system, the

A.        Minimum enthalpy and maximum entropy both favour the products.

B.         Minimum enthalpy and maximum entropy both favour the reactants.

C.        Minimum enthalpy favours the products and maximum entropy favours the reactants.

D.        Minimum enthalpy favours the reactants and maximum entropy favours the products.

16.       Which of the following describes how a Keq value is related to the relative concentrations of reactants and products?

Keq value                     Relative Concentration

I.          large                             [products] > [reactants]

II.         large                             [reactants] > [products]

III.       small                             [products] > [reactants]

IV.       small                             [reactants] > [products]

A.        I only

B.         IV only

C.        I and IV only

D.        II and III only

17.       Consider the following equilibrium: N2(g) +  O2(g)   2NO(g) +  25.6 kJ

Under certain conditions, Keq = 0.00056. When conditions are changed,

Keq becomes 0.0256. Which of the following could account for this?

A.        [N2] was changed.

C.        Temperature was decreased.

D.        Temperature was increased.

18.       Consider the following equilibrium: N2O(g)  +  NO2(g)     3NO(g)  + 120 KJ

Under certain conditions, Keq = 2.5. When conditions are changed, Keq becomes 0.15.

Which of the following could account for this?

C.        Temperature was decreased.

D.        Temperature was increased.

19.       Reacting systems tend toward which of the following?

Entropy            Enthalpy

A.        minimum           maximum

B.         minimum           minimum

C.        maximum        minimum

D.        maximum          maximum

20.       Consider the following equation: NH4NO3(g)    N2O(g)  +  2H2O(g) + 37 kJ

Which of the following is true?

Enthalpy Favours          Entropy Favours           Outcome

A.        reactants                       reactants                       does not occur

B.        products                      products                      completion

C.        reactants                       products                       equilibrium

D.        products                       reactants                       equilibrium

21.       Consider:          energy   +   N2O4(g)             2NO2(g)

The system above reaches equilibrium.  Considering enthalpy and entropy factors,

which of the following is true with respect to the forward reaction?

A.        The entropy is increasing and the reaction is exothermic.

B.         The entropy is decreasing and the reaction is exothermic.

C.        The entropy is increasing and the reaction is endothermic.

D.        The entropy is decreasing and the reaction is endothermic.

22.       Which of the following forward reaction changes would result in the most products?

Entropy            Enthalpy

A.        decreasing        decreasing

B.        increasing       decreasing

C.        decreasing        increasing

D.        increasing         increasing

23.       Which of the following forward reaction changes would result in the most reactants?

Entropy            Enthalpy

A.        decreasing        decreasing

B.         increasing         decreasing

C.        decreasing      increasing

D.        increasing         increasing

24.       Which of the following forward reaction changes would result equilibrium?

Entropy            Enthalpy

A.        decreasing      decreasing

B.         increasing         decreasing

C.        decreasing        increasing

D.        constant            constant

25.       When the temperature of an endothermic equilibrium is increased, which of the following will happen?

A.        Equilibrium will shift left and [products] will increase.

B.         Equilibrium will shift left and [products] will decrease.

C.        Equilibrium will shift right and [reactants] will increase.

D.        Equilibrium will shift right and [reactants] will decrease.

26.       When the temperature of an exothermic equilibrium is decreased, which of the following will happen?

A.        Equilibrium will shift left and [products] will increase.

B.         Equilibrium will shift left and [products] will decrease.

C.        Equilibrium will shift right and [reactants] will increase.

D.        Equilibrium will shift right and [reactants] will decrease.

27.       When the temperature of an endothermic equilibrium is increased, which of the following will happen?

A.        Equilibrium will shift left and the Keq will increase.

B.        Equilibrium will shift right and the Keq will increase.

C.        Equilibrium will shift left and the Keq will stay constant.

D.        Equilibrium will shift right and the Keq will stay constant.

28.       Consider:  2Li(s) +  H2O(l)   ®   2LiOH(aq)   +  H2(g)   ΔH = -256 kJ?

What will entropy and enthalpy factors favour?

Entropy            Enthalpy

A.        products           reactants

B.        products          products

C.        reactants           reactants

D.        reactants           products

29.       Consider:  3C(s)   +   3H2(g)     +   heat      C3H6(g)

What will entropy and enthalpy factors favour?

Entropy            Enthalpy

A.        products           reactants

B.         products           products

C.        reactants         reactants

D.        reactants           products

30.       In order for a chemical reaction to go to completion, how must the entropy and enthalpy change?

enthalpy            entropy

A.        increases          increases

B.         increases          decreases

C.        decreases       increases

D.        decreases         decreases