Chemistry 114
Third Hour Exam
Name:____________
(2 points)
Please show all work for partial credit
1. The reaction described by
2NO2(g)6 2NO(g) + O2(g)
is postulated to occur via the mechanism
(1) NO2(g) + NO2(g) 6 NO(g) + NO3(g)
(2) NO3(g) 6NO(g) + O2(g)
Slow
Fast
Experimentally the rate law for reaction was determined to by rate = k[NO2]3
(6 points) Is the proposed mechanism consistent with the observed rate law? Justify your
answer
The reaction described by the equation
2NO2(g) +Br2(g) 62NO2Br
Is postulated to occur via the following mechanism
(1) NO2(g) + Br2(g) W NO2Br2(g)
Fast equilibrium
(2) NO2Br2(g) 6NO2Br(g) + Br(g)
Slow
(3) Br(g) + NO2(g) 6NO2Br(g)
Fast
(6 points) Write the rate law, in terms of starting reactants, that you would expect for this
mechanism
2. If a cake bakes need to bake for 40 minutes at 350o(175oC) , but only needs to bake for
30 minutes at 400o (~205oC)
A. (6 points) What is the activation energy for baking a cake?
(Hint: use 1/40 min or .025 min-1 for the k at 350F, and 1/30 min or .033 min-1 for the
rate at 400)
B. (6 points) How long will it take to bake at 450o (~230oC)
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3. In the reaction A6B:
A has an energy of 5 kJ
The ÄH for the reaction is -7 kJ
A. (3 points) What is the energy of the product B? _______________
The uncatalyzed reaction has an activation energy of 15 kJ.
B. (6 points) Draw an activation energy diagram for this reaction. Make sure you
label all the axes and the important features of the diagram.
C. (3 points) When a catalyst is added, the reaction has an activation energy
of 10 kJ.
Include a curve for the catalyzed reaction in your plot above.
4. Define the following terms:
elementary step
intermediate
Steric factor
heterogenous catalyst
transition state
Le Châtlier’s Principle
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5. The reaction CH3COOH W CH3COO- + H+ has a KC of 1.75x10-5
A. If the system is in equilibrium and [CH3COOH]=[CH3COO-] = 0.001M,
(2 points) What is the [H+]?
B. If the [CH3COOH]=[CH3COO-] = [H+] = 0.001M
(1 point) Is the system at equilibrium?
(1 point) If it is not at equilibrium, will the concentration of H+ increase or
decrease as it moves toward equilibrium?
(2 points) Why?
C.
B. If the [CH3COOH]=[CH3COO-] = [H+] = 1x10-5M
(1 point) Is the system at equilibrium?
(1 point) If it is not at equilibrium, will the concentration of H+ increase or
decrease as it moves toward equilibrium?
(2 points) Why?
6. KP for the reaction PCl5(g) W PCl3(g) + Cl2(g) is 1.78 atm at 250o C.
(4 points) What is KP for the reaction 3PCl5(g) W 3PCl3(g) + 3Cl2(g)
(4 points) What is KC for the reaction PCl3(g) + Cl2(g) W PCl5(g)
(4 points) If KP for the reaction Cl2(g) W2Cl(g) is .578 bar, what is K P for the reaction
PCl5(g)WPCl3(g) +2Cl(g)
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7.
The reaction Mg2+ + EDTA4- W MgAEDTA2- has a KC of 7.85x109 at a certain pH.
If I have a solution that is .005M MgAEDTA-2
A. (2 points) Fill in the I part of the ice table below:
Mg2+ +
EDTA4W
MgAEDTA2-
I
_____
______
_______
C
_____
______
_______
E
_____
______
_______
B. (2 points) In which direction will the reaction go, right or left? (Circle one)
C. (2 points) Using +X or -X, fill in the C part of the ice table above.
D. (2 points) Fill in the E part of the ice table above.
E. (2 points) Write the equilibrium equation for the above system.
F. (2 points) Can you make any assumptions to solve the above expression?
Guess what, you don’t have to solve it. I have faith you can do it, I’ll even
give you two points for it!
8. (16 points) The reaction CO(g) + H2O(g) 6 CO2 (g) + H2(g), which has a ÄH of -90.7 kJ,
has come to equilibrium in a closed vessel. If I want to INCREASE the concentration of
H2 in the container
A. Will it matter if I change the concentration of CO in the container
YES or NO
(Circle one)
B. If your answer to the above is yes, then do I want INCREASE OR DECREASE the
concentration of CO?
(Circle one)
C. Will it matter if I change the concentration of CO2 in the container
YES or NO
(Circle one)
D. If your answer to the above is yes, then do I want INCREASE OR DECREASE the
concentration of CO2?
E. Will it matter if I change the volume of the container
YES or NO
F. If your answer to the above is yes, then do I want INCREASE OR DECREASE the
volume of the container?
G. Will it matter if I change the temperature of the container YES or NO
H. If your answer to the above is yes, then do I want INCREASE OR DECREASE the
temperature?
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