Quiz Four Practice, Chemistry 111, Lycoming College, Feb. 16, 2005, Dr. Mahler

 

Fair Game for Fridays Quiz: All previous material (Ch. 11, 12, 13). New Material Ch. 13 section 9, Chapter 14 Sections 1, 2 and 3. Relevant Homework: Ch. 13 all assigned, but especially 61, 65, 67, 68 and 85c (all mechanisms); Ch. 14 problems 22, 25, 29, 32, 35, 38 and 41 (keys on web: http://www.lycoming.edu/chem/spring2005/111/keys.htm)

 

Practice problems:

 

1) Possible essay / short answer type questions:

 

2) A reaction was believed to occur by the following mechanism:

 

Step 1)             A2 A + A and its reverse, A + A A2

Step 2)             A + A + B A2B

Step 3)             A2B + C A2C + B

 

a) Write the overall reaction. b) Write the rate law for each step and indicate its molecularity. c) Identify each species as a reactant, product, intermediate, or catalyst.

 

3) The following mechanism has been proposed for the reaction of chlorine and chloroform, CHCl3:

 

Step 1)             Cl2 Cl + Cl and its reverse, Cl + Cl Cl2                 (both fast)

Step 2)             CHCl3 + Cl CCl3 + HCl                                                      (slow)

Step 3)             CCl3 + Cl CCl4                                                       (fast)

 

Write the rate law based on this mechanism, clearly stating any assumptions / reasoning.

 

4) Write the expression for Kc for each of the following reactions:

a) NH4HS (s) NH3 (g) + H2S (g)

b) ZnO (s) + CO (g) Zn (s) + CO2 (g)

c) SbCl5 (g) SbCl3 (g) + Cl2 (g)

d) H2 (g) + I2 (g)  2 HI (g) 

 

5) Calculate the following (all at equilibrium):

a) The concentration of H2 (g) in reaction 4d), above, if at 500 K, Kc = 160, [HI] = 2.21 mmol/L, and [I2] = 1.46 mmol/L.

b) At 500 K, Kc = 3.5 x 10-4, [SbCl5] = 0.15 M, [SbCl3] = 0.20 M. What is [Cl2]? See 4c).