Chemistry 112

Exam 2

 

Name _____________________________

 

Show all of your work.  R = 8.314 J/K mole or 0.08206 L atm/mole K

 

1.  If  K = 8.35 x 105 for the reaction:  2H2 (g)  +  S2 (g)  Û  2 H2S (g)

  What is K  for:  H2S (g)  Û   H2 (g)  +  ½ S2 (g)?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.  0.50 M H2S, 1.0 x 10−4 M H2 and 0.40 M S2 (2H2 (g)  +  S2 (g)  Û  2 H2S (g)) are mixed at 525 °C where K = 8.35 x 105.  Is this mixture at equilibrium?  If not, in which direction will it shift?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.  For the reaction NH4OCONH2 (s) Û 2NH3 (g)  +  CO2(g), Kp = 3.0 x 10-6?

What are the equilibrium pressures of NH3 and CO2?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4.  The reaction:  NH4OCONH2 (s) Û 2NH3 (g)  +  CO2(g)  is endothermic.  How will the equilibrium shift if:

 

(A)  The temperature is increased?

 

 

 

(B)  The volume of the reaction flask is decreased?

 

 

 

(C)   NH4OCONH2 is added?

 

 

 

(A)     NH3 is removed?

 

 

 

(F)  A catalyst is added?

 

 

 

5.  4.0 atm of S8 is placed in a empty flask where it decomposes by:  S8(g)  Û  4 S2(g)

If the partial pressure of S2 at equilibrium is 0.50 atm, what is Kp for the reaction?

 

 

 

 

 

 

 

 

 

 

 

 

6.  A sample of radioactive 59Fe has an initial activity of 125 counts/second.  After 10.0 days, the sample has an activity of 107 counts/second.  What is t½ for 59Fe?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7.  The following data were collected for the reaction of:

 2OH¯  +  2ClO2  ®  ClO3¯  +  ClO2¯   +  H2O

 

Run

Initial [ClO2]

Initial [OH¯]

Initial Rate M/s

1

0.60

0.30

.0248

2

0.20

0.30

.00276

3

0.20

0.90

.00828

 

(A)    What is the rate law for the reaction?

 

 

 

 

 

 

 

 

 

(B)    Calculate k

 

 

 

 

 

 

 

8.  The following mechanism has been proposed for the reaction of NH2NO2 :

 

            1.  NH2NO2  +  OH¯  →   H2O  +  NHNO2¯                         slow

            2.  NHNO2¯  →  N2O   +  OH¯                                                          fast

 

(A)  What is the overall reaction?

 

 

 

(B)  List all intermediates.

 

 

 

 

(C)  List all catalysts.

 

 

 

(D)  What is the rate law predicted by this mechanism?

 

 

 

 

 

9.  Some old mammoth bones were dated using 14C and found to be 11300 years old.  If the activity of a new sample is 15.3 counts/min and t1/2  (14C) is 5730 years, what was the activity for the bones?