AP Chemistry Chapter 13 & 15 Free Response Exam 2015
Name ____________________________
II. 50% of your grade will come from these two questions. You may use a calculator with this section. You
will have 40 minutes for this section of the test.
1. The equilibrium constant in terms of pressure, Kp, for the reaction
4.1 x 104 at 25◦C.
3 H2(g) + N2(g)  2 NH3(g) is
a.
Write the equilibrium expression for this reaction.
b.
The three gases were placed into an otherwise empty flask at the following pressures. The flask was
then sealed and brought to 25◦C : PNH3 = 3.1x 10-2 atm ; PN2 = 8.5 x 10-1 atm ; PH2 = 3.1 x 10-3 atm. In
which direction does the overall reaction proceed? You must provide a mathematical justification for
your answer.
c.
Substitute all of the appropriate equilibrium values into the equilibrium expression in order to findthe
equilibrium pressures of all three gases. YOU DO NOT NEED TO SOLVE FOR THEEQUILIBRIUM
PRESSURES.
d.
Solve for the value of Kc at 25◦C
e. What would happen to the concentration of N2 gas if the volume of the container was decreased?
Justify your answer.
f.
At 300◦C, the Kp of the original reaction is 3.3 x 106. Is the reaction endothermic or exothermic?
Explain.
g.
Kp for a second reaction:
N2(g) + 2 H4Cl(g)  2 HCl(g) + 2 NH3(g )
What is the Kp value for the reaction: 6 H2(g) + 6 HCl(g) + 2 NH3(g) 
is 1.7 x 10-3.
N2(g) + 6 H4Cl(g)
2. The solubility product constant, Ksp, for Cu2(CO3) is 2.7 x 10-9.
a.
Write a solubility constant expression for the dissociation of Copper (I) carbonate.
b.
Calculate the molar concentration of both the copper (I) and the carbonate ions in 200 mL of a saturated
solution of Cu2 (CO3) and clearly label both.
c.
Which is more soluble, Copper (I) carbonate of Copper (II) carbonate? The Ksp of Copper (II)
carbonate is 1.3 x 10-8. Justify your choice.
d.
If 1.00 mL of .25 M Copper (II) Chloride solution is mixed with 2.00 mL of .40 M sodium carbonate,
will a precipitate of Copper (II) carbonate form. Support your answer with a calculation.
e.
A student has a solution which is a mixture of .2 M Ba2+ and .2 M Sr2+ ions. They want to try to
separate the two ions by selectively precipitating them with sulfate ions. The Ksp of barium sulfate is 1.6
x 10-15 and the Ksp of strontium sulfate is 5.2 x 10-8. The barium sulfate begins to precipitate first.
What is the concentration of the barium 2+ ions when the strontium sulfate begins to precipitate?