CHEMISTRY 21A
Instructor: Dr. Dragan Marinkovic
Assignment #9
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Student Name / registration number
1. a) What is a reaction rate and what is the mathematical expression (equation) for it?
b) A stable substance is:
c) A spontaneous process is:
d) An endergonic process is:
e) Entropy is:
2. What is a reaction mechanism?
3. What ia activation energy?
4. Draw the following energy diagrams:
a) an endothermic reaction with a moderate activation energy
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Date
CHEMISTRY 21A
Instructor: Dr. Dragan Marinkovic
Assignment #9
b) an exothermic reaction with no activation energy
c) an exothermic reaction showing different activation energies without and with use of a catalyst
5. Define Le Chatelier’s principle.
6. UsinWhat factors influence reaction rates?
7. What is
a) a catalyst?
b) an inhibitor?
c) a state of equilibriium?.
d) a heterogeneous catalyst?
e) an equilibrium concentration?
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CHEMISTRY 21A
Instructor: Dr. Dragan Marinkovic
Assignment #9
8. For the following reaction:
N2(g) + 3H2(g) ⇌ 2NH3(g)
draw the following reaction diagrams:
a) Reaction rate vs. time
b) Concentrations (of reactants and products) vs. time
9. The equilibrium constant for the reaction:
PCl5 ⇌ PCl3 + Cl2
is 0.0245 at 250oC. What molar concentration of PCl5 would be present if concentrations of both PCl3 and Cl2 were
0.250 M?
10. Tell what happens with each equilibrium concentration in the following reactions when the stress is applied and the new
equilibrium position is established:
a) H+(aq) + HCO3-(aq) ⇌ H2O(l) + CO32-(aq)
HCO3- is added
b) CO2(g) + H2O(l) ⇌ H2CO3(aq) + heat
CO2 is removed
c) CO2(g) + H2O(l) ⇌ H2CO3(aq) + heat
the system is cooled
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CHEMISTRY 21A
Instructor: Dr. Dragan Marinkovic
Assignment #9
11. Consider the following equilibrium constants. Describe how you would expect the equilibrium concentrations of
reactants and products to compare with each other (larger than, smaller than, etc., for each case):
a) K = 5.9
b) K = 2.7x10-4
c) K = 0.0000558
12. The following equilibria are established in water solutions Write an equilibrium expression for each reaction.
a) Fe3+ + 6CN- ⇌ Fe(CN)63-
b) Ag+ + 2NH3 ⇌ Ag(NH3)2+
c) Au3+ + 4Cl- ⇌ AuCl4-
13. A reaction is run at 20oC and it takes 30 minutes to go to completion. How long would it take to complete the same
reaction at 40oC?
14. Suppose a small lake is contaminated with an insecticide that decomposes with time. An analysis done in June
showed the decomposition product concentration to be 7.8x10 -4 mol/L. An analysis done 35 days later showed the
concentration of the decomposition product to be 9.9x10-4 mol/L. Assume the lake volume remains constant and calculate
the average rate of decomposition of the insecticide.
15. Colorless hydrogen and red-brown bromine gases react to form colorless HBr gas. Describe how the concentrations of
H2, Br, and HBr would change (increase or decrease) in a sealed container that initially contained only H2 and Br2 as
equilibrium was established. What observation would indicate that equilibrium had been established?
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