Dr. Herrick's CH223
Pressure Quiz 1

     

 

                              

Chemical Equilibrium
Copyright D. Herrick

 

20 Questions from past exams.
Practice for speed.  Aim for 2 minutes per problem.

 

                              

Ideal gas constant:  R = 0.08206 L-atm/mol-K = 8.314 J/mol-K
 
1. Determine the standard Kc expression for the reaction

   C(s) + 2 N2O(g) CO2(g) + 2 N2(g)
A)   [C][N2O]2 F)   [CO2]1/2[N2] / [N2O]
B)   [N2]2[CO2] / [N2O]2 G)  [N2]2[CO2] / [N2O]2[C]
C)   [CO2][N2]2 H)  2[N2] - [CO2] - 2[N2O]
D)  1/[C] I)    [N2O]-1/2[CO2][N2]1/2
E)   [N2O]2 [CO2][N2]2 J)   [C]-1[N2]2[CO2][N2O]-2

                              

2. An equilibrium mixture for the reaction

2A(g) + 3B(g) C(g) + 5D(g)

has 0.250 M A, 0.125 M B, 2.000 M C and 0.500 M D. The value of Kc is:

A) 128 B) 0.063 C) 512 D) 32.000 E) 5.143
F) 256 G) 266.7 H) 1.000 I) 2.000 J)  zero

                              

3. 3 mol of A and 2 mol of B placed in a 1-liter vessel react to equilibrium according to the gas-phase reaction

    2 A + B 3 C

If "x" denotes the mols of B reacted, then the expression for Kc is:

A)    D)
B) E)
C)    F)

 

4. The reaction 2A(g) B(g) has KP = 16.  If the equilibrium pressure of B is 9 atm, the pressure of A (atm) is:
A) 1296 B) 0.56 C) 144 D) 1.33 E)  0.50
F)  6.00 G)  0.38 H) 8.25 I) 1.50 J)  0.75

                              

5. Determine the concentration (M) of NO2 after 1.00 mol of N2O4 placed in a 1.00-liter flask comes to equilibrium according to the reaction

   N2O4(g) 2 NO2(g) ,   Kc = 2.000
    
A) 0.618 B) 1.125 C) 2.000 D) 0.732 E)  1.000
F) 0.000 G) 0.500  H) 1.236 I) 1.414 J) 0.250 

                                 

6.

Use the reactions

 H2S + H2  H3O+ + HS-
  K1 = 1 10-7  

 HS- + H2  H3O+ + S2-  ,   K2 = 1 10-17 

to find K for

 
H2S + 2H2O   2H3O+ + S2-  
      

A)    1 1010   D) 1 10-3
B) 1 1024   E) 1 10-10 
C)    1 103   F) 1 10-24 

   

7.

Use the reactions

 HCN + H2O   H3O+ + CN-  K1 = 1 10-10  

 2H2O   H3O+ + OH-  K2 = 1 10-14 

to find K for the acid-base neutralization

 OH- + HCN     H2O + CN- 

  

A)    1 1014   D) 1 10-4
B) 1 1024   E) 1 10-14 
C)    1 104   F) 1 10-24 

    

              

8. The gas phase equilibrium reaction

 3 H2(g)  +  N2(g)    2 NH3(g) 

has Kc = 0.0024 at 1000K.   When 2 mol of H2, 5 mol of N2, and 3 mol of NH3 are mixed in a 100-liter vessel at 1000K the result is:

A) produce more hydrogen and nitrogen from ammonia.
B) convert hydrogen and nitrogen into more ammonia.
C) no reaction, the starting mixture is at equilibrium.
D) the concentration of each reactant and product doubles.
E) the concentration of each reactant and product is halved

                              

9. Given the equilibrium constants for the reactions

  4Cu(s) + O2(g) 2Cu2O(s),  K1

  2CuO(s) Cu2O(s) + 0.5 O2(g),  K2

what is K for the reaction

 2Cu(s) + O2(g) 2CuO(s) ?

A) K11/2 K2
B) K1 K21/2
C) K21/2 / K1
D) K11/2 / K2
E) K1 K2

   

Questions 10-14 consider an equilibrium mixture for  the heterogeneous reaction

 2 C(s)  +  O2(g)   2 CO(g)     (exothermic)
   

           

10. How does the equilibrium shift when additional O2 is added?
A) 2 C +  O2  2 CO
B) 2 C +  O2   2 CO
C) no shift

  

11. How does the equilibrium shift when the total pressure is increased?
A) 2 C +  O2   2 CO
B) 2 C +  O2   2 CO
C) no shift

  

12. How does the equilibrium shift when the temperature is increased?
A) 2 C +  O2  2 CO
B) 2 C +  O2   2 CO
C) no shift

    

13. How does the equilibrium shift when additional C is added?
A) 2 C +  O2  2 CO
B) 2 C +  O2   2 CO
C) no shift

  

14.

The conversion  Kp = Kc (RT)b  for this reaction has b=
       

A) 5 B) 4 C) 3 D) 2 E)  1
F) 0 G) -1 H) -2 I) -3 J) -4

  

15. Which change would cause the following equilibrium to shift to the right?

  2NOBr(g) 2NO(g) + Br2(g),   Ho  = 30 kJ
 

A) Decrease the volume of the reaction vessel.
B) Add some NO.
C) Remove some NOBr.
D) Add Br2.
E) Increase the temperature.

  

16. Determine Kc for the heterogeneous equilibrium at 500K:

 A(s) + 3B(g)  2C(l) + 2D(g),   Kp = 0.136
  

A) 3.34 B) 56.5 C) 14.6 D) 0.136 E)  5.58

  

17. How does the reaction shift when a catalyst is added to an equilibrium mixture? 
 
 N2(g) + 3H2(g) 2NH3(g) ,   Ho  = -92 kJ
 
A) N2 + 3H2  2NH3
B) N2 + 3H2   2NH3
C) no shift

  

18. If the reaction N2 + 2H2O  2NO + 2H2 has Kc = 1 10-2  then the reaction

  NO + H2 N2 + H2O

has Kc =  

A)    1   D)   1 10-2
B)    1 10+1  E)    1 10-1
C)    1 102   F)    1 103 

  

19.

Predict the reaction direction when  [CS2] = [H2] = [CH4] = [H2S] = 0.125 M:

 CS2(g) + 4 H2(g) CH4(g) + 2 H2S(g)  ,     Kc = 28
 

A) reactants  products
B) reactants   products
C) no change--the system is already at equilibrium

  

20. 5 mole of AB is placed in a 1.00 L reaction vessel and is allowed to come to equilibrium according to the reaction

  AB(g) A(g) + B(g),   Kc = 7.00

Determine the degree of dissociation of AB in the final equilibrium mixture.
  

A) 73%
B) 99%
C) 41%
D) 67%
E) 54% 
F) 4.8%

                              

 

 

   Copyright  D. Herrick