Download Exam 2 - Practice

CHM136: Practice for Exam 2 (Spring 2015)
1. Consider the following second-order decomposition reaction with rate constant:
2 HCl  H2 + Cl2
k = 1.65 x 10-2 L mol-1 sec-1
If the initial concentration of HCl is 0.100 M, what will be the concentration of HCl after
2.00 minutes?
2. Consider the first-order decomposition reaction:
2 NO ----> N2 + O2
If the rate constant is 8.3 x 10-3 sec-1, how long will it take for 75% of the NO to react?
3. Consider the following initial rate data:
CO2 + 2 Cl2 ----> CCl4 + O2
[CO2]
[Cl2]
initial rate [mol/L-sec]
0.16
0.32
0.0128
0.16
0.45
0.0180
0.56
0.45
0.0630
Write down the rate law for this reaction. Evaluate all reaction orders and also the rate
constant. Express the rate constant in appropriate units.
4. Consider the following bimolecular reaction with stated rate law:
rate = k [NO2]2
2 NO2 + 3 I2 ----> 2 NI3 + 2 O2
Circle which one of the following mechanisms is consistent with the rate law for this
reaction:
Mechanism A
NO2 + NO2----> NO2 + O2 + N
(slow)
N + NO2
----> O2 + 2 N
(fast)
2 N + 3 I2
----> 2 NI3
(fast)
Mechanism B
NO2 + I2
----> NI2 + O2
NO2 + NI2 ----> O2 + 2 NI
2 NI + 2 I2----> 2 NI3
(slow)
(fast)
(fast)
5. Consider the following chemical equilibrium:
2 NO 2 (g) ←→ 2 NO (g) + O 2 (g)
At equilibrium, the following partial pressures were recorded:
PNO 2 = 50.0 atm
PNO = 0.00100 atm
PO 2 = 0.00100 atm
Calculate the equilibrium constant for this reaction (include units):
6. Suppose 2.00 atm of COCl2 are introduced into an empty vessel. Calculate the
equilibrium partial pressures of all three gases. (Kp uses atm as reference)
COCl2 (g) ↔ CO (g) + Cl2 (g)
KP =
4.5
7. What is the effect of increasing total pressure on an equilibrium mixture of diatomic and
monatomic fluorine gas?
Circle one:
a. F2 will increase
F2 (g) ↔ 2 F (g)
b. F will increase
c. no effect
8. What is the effect of adding additional hydrogen gas to an equilibrium mixture defined
as:
Circle one:
a. CH4 will increase
2 CH 4 (g) ↔ C2 H 2 (g) + 3 H 2 (g)
b. CH4 will decrease
c. no effect on CH4
−2
−1
9. A certain first-order reaction has a rate constant equal to 1.85 × 10 sec at 25.0 oC. At
−2
−1
95.0 oC the rate constant is 9.76 × 10 sec . What is the energy of activation? What is the
frequency factor? What is the rate constant at 125. oC?
The equilibrium constant for the reaction 2 Br (g) <-> Br2 (g) is Kp= 2.78 x 1012. What is the equilibrium constant of
the reverse reaction, Br2 (g) <-> 2 Br (g)? circle one:
a. – 2.78 x 1012
b. 3.60 x 10-13
c. 1.39 x 1012
10.
11. The equilibrium constant for the reaction 2 Br (g) <-> Br2 (g) is Kp= 2.78 x 1012.
this reaction: 1/2 Br2 (g) <-> Br (g)? circle one:
a. – 1.39 x 1012
b. 1.80 x 10-13
c. 6.00 x 107
What is the equilibrium constant of
d. 6.00 x 10-7
12. The reaction below is prepared with an initial pressure of hydrogen sulfide, H2S, of 2.50 atm and an initial
pressure of sulfur dioxide, SO2, of 2.00 atm. At equilibrium you determine that the pressure of the sulfur
dioxide has decreased to only 0.82 atm. Determine Kp for the reaction.
2 H2S(g) + SO2(g)
↔
3 S(s) + 2 H2O(g)