Chemistry 114
Third Hour Exam
Name:____________
(4 points)
Please show all work for partial credit
1. (12 points) I am studying a reaction with an overall stoichiometry of 2A + C 6 D.
Five mechanisms have been proposed for this reaction:
Mech I
Mech II
Step 1 A + A + C 6D
Step 1.
A+A6B
Slow
Step 2.
B+C6D
Fast
Mech III
Mech IV
Step 1. A + C 6B Slow
Step 1. A + C 6B Slow
Step 2. B + A 6D Fast
Step 2. B + C 6D Fast
Mech V
Step 1. A + C 6B Fast equilibrium
Step 2. B + A 6D Slow
A. Which mechanism(s) can be rejected based on the stoichiometry of the reaction?
__IV_____________
B. Which mechanism(s) can be rejected if the experimental kinetics shows that
rate =k[A]2 ?
____I,III,IV,V____________
C. Which mechanism(s) can be rejected if the experimental kinetics shows that
rate =k[A][C]2?
___All_____________
D. Which mechanism(s) can be rejected if the experimental kinetics shows that
rate =k[A][C]?
____I,II,V____________
E. Which mechanism(s) can be rejected if the experimental kinetics shows that
rate =k[A]2[C]?
____II,III,IV____________
2. (12 points) I have a reaction that has a rate constant (k) of .085 M@sec-1 at 25oC. If the
rate for this reaction is .25 M@sec at 35oC, what is the activation energy of this reaction?
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3. (12 points) In the following diagram
What is the ÄH for the reaction? ___-4 kJ_______
What is the Ea of the reaction?
___+4 kJ__________
What is the energy of the reactants?
___+6 kJ________
What is the energy of the products?
___+4 kJ________
What is the energy of the activated complex? __+10 kJ________
(The actual figure was drawn by hand on the original test!)
4. (12 points) Define the following terms:
Heterogenous catalyst
A catalyst is substance that speed up a reaction, but is not consumed in the reaction, a
heterogeneous catalyst is in a different phase than the reactants and products.
Reaction mechanism
A series of elementary steps that, when summed, equals the stoichiometric equation for
a reaction, and describe the individual collisions that occur in a given reaction.
Collision Frequency
The z factor in the equation k=zñe-ea/RT that gives the total number of collisions that
can occur.
Le Châtelier’s principle
If a system that is at equilibrium is changed, the system will respond in a way to
minimize that change.
Arrhenius Acid
Produces H+
Electrophile
An electron loving substance, or an electron acceptor, or a Lewis base.
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5. (12 points) Write equilibrium expressions for the following reactions:
N2(g) + 2O2(g) W 2NO2(g)
Ca(IO3)2(s) W Ca2+(aq) + 2IO3-(aq)
CH3COOH(aq) + H2O(l) WCH3COO-(aq) + H3O+(aq)
CaCO3(s) WCaO(s) + CO2(g)
K=[CO2]
6A. (4 points) Your body hydrolyzes ATP to make ADP and Pi in the reaction:
ATP + H2O WADP + Pi KC = 3.5x104 M.
What is the Kc for the reaction ADP + Pi WATP + H2O?
K of reverse reaction = 1/K of forward
=1/3.5x104 = 2.86x10-5 M-1
B. (4 points) When your body uses glucose to make ATP, the first step of the process,
surprisingly, is to use ATP to make glucose-6-phosphate in the reaction:
Glucose + ATP W Glucose-6-phosphate + ADP.
Use the reaction:
Glucose + PiW Glucose-6-phosphate + H2O
KC 6.9x10-3 M-1
And the information in part A to determine the KC for the reaction:
Glucose + ATP W Glucose-6-phosphate + ADP.
If you add the equations together, then you multiply the Ks
K = K1 x K2
=3.5x104 x 6.9x10-3 = 241
C. (4 points) Use your answer from part B above to determine KC for the reaction:
3Glucose + 3ATP W 3Glucose-6-phosphate + 3ADP.
(Help: If you don’t have an answer for part B above, assume the answer for B is 5x103)
If you change all the coefficients by a factor then your raise the K to that power
K = K3
=2413 = 1.4x107
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7.At 900K the equilibrium constant for the equation
2SO2(g) + O2(g) W 2SO3(g)
is 13 M-1
If I mix the above gases in a container so their concentrations are:
[SO2]= .1M [O2]= .3M
[SO3]=.4M
A. (1 point)Will the reaction move toward products or reactants?
Reactants
B. (3 points) WHY?
Q = (.4)2/(.12 A.3) = 53, Q>K, too many products, need to make more reactants
C. (4 points) Fill in the following ICE table
2SO2(g)
+
O2(g) W
I
__.1______
____.3____
C
__+2X_____
____+X____
E
__.1+2X___
____.3+X__
2SO3(g)
__.4______
___-2X____
___.4-2X___
D. (4 points) Write the equilibrium equation you need to use to solve for X in part C:
(Do NOT try to solve the equation)
8. (12 points) The reaction 2NH3 W N2 + 3H2 has a ÄH of +92 kJ/mol. If the reaction is at
equilibrium at 25oC in a 5 L container that also contains CO2, but I want to decrease the
amount of N2 in the container.
Will it matter if I change the amount of NH3 in the container? Yes or No (Circle one)
Should I increase or decrease the amount of NH3 in the container? (Circle one)
Will it matter if I change the amount of H2 in the container? Yes or No (Circle one)
Should I increase or decrease the amount of H2 in the container? (Circle one)
Will it matter if I change the amount of CO2 in the container? Yes or No (Circle one)
Should I increase or decrease the amount ofCO2 in the container? (Circle one)
Will it matter if I change the volume of the container? Yes or No (Circle one)
Should I increase or decrease the volume of the container? (Circle one)
Will it matter if I change the temperature of the container? Yes or No (Circle one)
Should I increase or decrease the temperature of the container? (Circle one)
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