PRESEMESTER EXAM
KINETICS AND EQUILIBRIUM AND THERMODYNAMICS
1. A set of kinetic experiments were performed on the reaction: A + 2 B  2C, and the following data were obtained<
Trial
[A]
[B]
1
2
3
.100
.100
.200
.400
.800
.800
Initial rate of formation of C
(M s1-)
.0200
.0200
.080
a. Determine and state the order of the reaction with respect to each reactant and write the overall rate law for this
reaction.
b. Calculate the value and units of the rate constant.
c. If the temperature is increased by 10 Ko and trial 3 is repeated, what would you anticipate to be the initial rate of
formation of C, why?
d. Prove whether or not the proposed mechanism is consistent with the rate law for the reaction. If it is not, suggest a
mechanism that might be.
Step 1: A  2 I (I is the intermediate) SLOW
Step 2: B + I  C
FAST
Step 3: B + I  C
FAST
2. If a rate law for a reaction is found to be: r= k[A]2
a. draw a graph representing r vs. [A]
b. draw the integrated rate law graph (label axes)
c. describe how this graph could be used to determine the value of “k”
d. how could you determine the half-life of the reaction.
3. The solubility of silver chromate is .0280 g/L.
a. Write the chemical equation for the dissolution of silver chromate, AND the equilibrium expression for this process.
b. Determine the value of Ksp.
c. The Ksp of silver chloride is 1.8 x 10-10. What is the solubility in mol/L and g/L.
d. What is the minimum concentration of sodium chromate needed to form a precipitate of silver chromate in a
saturated AgCl solution.
4. hydrogen bromide decomposes : 2 HBr(g)  H2 )g) + Br2(g)
A. write the equilibrium expression (1) in terms of concentration and (2) in terms of pressure
B. A 55.5 g sample of HBr (M=80.9 g/mol) is transferred to a 22.0 L flask at 142 oC.
1. what is the initial concentration of HBr and 2. What is the initial pressure of HBr
C. When equilibrium is established, 22.4 g of Br2 is found in the flask. Calculate (1) Kc and (2)Kp
D. At another temperature, Kc= 17.7. 1.37 mol HBr, 2.31 mol H2 , and .551 mol Br2 are introduced into a 15.0 L flask.
Determine whether the reaction proceeds in a forward or reverse direction.
5. Given the reaction:
N2 + 3 H2  2 NH3 (∆Ho = -46.0 kj/mol)
a. completely summarize LeChatlier’s Principle.
b. What changes in concentration will increase the amount of ammonia produced?
c. What changes in pressure will NOT increase the amount of ammonia produced?
d. How should the temperature be changed to increase the amount of ammonia produced?
e. Will a catalyst increase the amount of NH3 produced, explain.
f. What will happen if liquid water is present in the reaction system?
6. The solubility of Fe(OH)2 is .00143 g/L.
a. write the equation for the solubility equilibrium
b. what is the solubility in mol/L
c. write the Ksp expression AND calculate Ksp
d. Calculate the pH of a saturated solution.
e. a 50.0 mL sample of .00200 M FeSO4 solution is added to 50.0 mL of .00300 M NaOH solution.
Determine whether or not will a precipitate form.
f. How is solubility of affected is if the pH of the solution is lowered. Use calculations to support your answer.
Presemester exam Thermodynamics:
1.
C(s)
CO2 (g)
H2(g)
H2O(l)
O2(g)
CH4 (g)
Standard Heat of Formation
(kJ/mol)
0
-393.5
0
-285.85
0
-74.9
Absolute entropies
(J/mol oK)
5.69
213.6
130.6
70
205.0
186.2
Use the above table to determine:
a. The heat of combustion of CH4
b. the balanced equation for the formation of CH4 from its elements
c. The standard entropy change for the formation for methane
d. the standard free energy of formation for methane
2.
a.
b.
c.
d.
Consider the dimerzation of NO2:
2 NO2  N2O4
Using Lewis structures, explain why NO2 dimerizes and CO2 does not.
What is the sign of the entropy change for the forward reaction. Explain.
at 100oC Kc = 3.3. What is the sign for ∆Ho?
Can the reverse reaction be made spontaneous? If so, how?
3. All of the following question concern the combustion of butane (C4H10)
a. Write the balanced reaction for the combustion of butane.
b. What volume of oxygen would be consumed, measured at .965 atm and 20.0 oC, when 10.0 g of butane is burned?
c. Using the chart below and given the fact that ∆Hocomb of butane is -2874.5 kJ mol-1, determine the standard heat of
formation of butane.
Standard Heat of Formation
(kJ/mol)
H2O(l)
-285.85
CO2 (g)
-393.5
d. If the energy is from the combustion of 1.00 mol of butane is transferred to water and the water temperatures rises
from 15.0 to 70.0oC,what is the mass of the water. (c water = 4.184 J/g oC)