# 1 1. Consider the following three equilibria occurring simultaneously

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Consider the following three equilibria occurring simultaneously in solution.
Ca2+ (aq) + C2O42– (aq)
CaC2O4 (s)
(1)
H2C2O4 (aq)
H+ (aq) + HC2O4– (aq)
(2)
HC2O4– (aq)
H+ (aq) + C2O42– (aq)
(3)
a) (2 pts) If NaOH is added to the solution, what reaction occurs? Write the net ionic equation for the
reaction that occurs when NaOH is added to the solution.
b) (2 pts) When NaOH is added to the solution, what is the affect on equilibrium (2). Does equilibrium (2)
shift to the right, to the left or is there no shift? Circle the correct answer.
Left
Right
No shift
c) (2 pts) When NaOH is added to the solution, what is the affect on equilibrium (3). Does equilibrium (3)
shift to the right, to the left or is there no shift? Circle the correct answer.
Left
Right
No shift
d) (2 pts) If there is a shift in equilibrium (2) or (3), how does this affect equilibrium (1). Does equilibrium (1)
shift to the right, to the left or is there no shift? Circle the correct answer.
Left
Right
No shift
e) (2 pts) Will the amount of CaC2O4 (s) precipitate increase or decrease? Circle the correct answer.
Increase
2.
(6 pts) Write the equilibrium constant expression, Kp, for each of the following equilibria.
a)
CaCl2 (s) + 2 H2O (g)
b) 2 NCl3 (g)
3.
CaCl2•2H2O (s)
N2 (g) + 3 Cl2 (g)
(6 pts) Predict how the equilibrium will shift by the affect of compression (a decrease in volume) for each of
the following systems. Circle the correct answer for each system.
a)
CaCl2 (s) + 2 H2O (g)
b) 2 NCl3 (g)
4.
Decrease
CaCl2•2H2O (s)
N2 (g) + 3 Cl2 (g)
left
right
no shift
left
right
no shift
(8 pts) The equilibrium constant K = 1.4 x 10–3 at 25oC, for the following reaction.
2 HI (g)
H2 (g) + I2 (g)
The initial concentrations are: [H2]o = 0.20 M, [I2]o = 0.25 M and [HI]o = 0.50 M. Calculate the reaction
quotient Q to determine the direction the reaction proceeds in order to reach equilibrium? Show your work.
1
5.
(10 pts) Consider the following equilibrium.
2 NOCl (g)
2 NO (g) + Cl2 (g)
The equilibrium constant, K = 1.6 x 10–5 at 400 oC. NOCl and Cl2 are placed in a 1-Liter container. The initial
concentration of NOCl is 1.0 M and the initial concentration of Cl2 is 1.0 M. Calculate the equilibrium
concentration of NO.
6.
(10 pts) For the thermal decomposition of CaCO3, the equilibrium constant Kp = 1.16 at 800 oC.
CaCO3 (s)
CaO (s) + CO2 (g)
If a 20.0-gram sample of CaCO3 is put into a 10.0-liter container and heated to 800oC, what percent of the
CaCO3 will react to reach equilibrium.
2
7.
8.
(10 pts) The density of a diatomic gas is 1.696 g/L at STP. Identify the gas.
(10 pts) Four identical 1.0-liter flasks contain the gases, He, CH4, Cl2, and NH3, each at 1 atm, and 25oC.
Circle one answer for each of the following questions.
a)
Which gas has the highest density?
He
CH4
Cl2
NH3
all gases the same
Cl2
NH3
all gases the same
Cl2
NH3
all gases the same
b) For which gas do the molecules have the highest average velocity?
He
c)
CH4
Which gas sample has the greatest number of molecules?
He
CH4
d) Which gas sample has the lowest frequency of collisions of gas molecules with each other?
He
e)
Cl2
NH3
all gases the same
For which gas do the molecules have the smallest average kinetic energy?
He
9.
CH4
CH4
Cl2
NH3
all gases the same
(10 pts) Calculate the temperature at which the average kinetic energy of O2 gas is twice that of He gas at 10oC.
3
10.
(10 pts) A mixture of KCl and KClO3 weighing 1.8 grams was heated. After the reaction goes to completion,
the O 2 gas generated occupied 140 mL at STP. Calculate the percent of the original mixture that was KClO3.
KClO3 decomposes according to the following reaction.
2 KClO3(s) —&gt; 2 KCl (s) + 3 O2 (g)
11.
(10 pts) The oxidation of nitric oxide to nitrogen dioxide occurs according to the following reaction.
2 NO (g)
+
O2 (g)
—&gt;
2 NO2 (g)
100.0 mL of NO at STP reacts with 400.0 mL of O2 at STP. The reaction goes to completion. Calculate the
partial pressure of NO2 in the final mixture if the total pressure is 1 atm.
4
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