Chemistry 213
Spring 2015
Exam II - A
Name_______________________________________
MATCHING (1 point each). Choose the item in column 2 that best matches each item in column 1.
1) The equilibrium-constant expression
for a reaction written in one direction
is the __________ of the one for the
reaction written for the reverse
direction.
2) Pure __________ and pure
__________ are excluded from
equilibrium-constant expressions.
A) solids, liquids
1)
B) products
C) reactants, products
D) reciprocal
2)
3) If the value for the equilibrium
constant is much greater than 1, then
the equilibrium mixture contains
mostly __________.
3)
4) If the reaction quotient Q for a
reaction is less than the value of the
equilibrium constant K for that
reaction at a given temperature,
__________ must be converted to
__________ for the system to reach
equilibrium.
4)
MULTIPLE CHOICE (1 Point Each). Choose the one alternative that best completes the statement or answers the
question.
5) At equilibrium, __________.
A) the rates of the forward and reverse reactions are equal
B) the rate constants of the forward and reverse reactions are equal
C) all chemical reactions have ceased
D) the value of the equilibrium constant is 1
E) the limiting reagent has been consumed
1
5)
6) The equilibrium constant for the gas phase reaction
2NH3 (g)
6)
N2 (g) + 3H2 (g)
is Keq = 230 at 300 °C. At equilibrium, __________.
A) only reactants are present
B) roughly equal amounts of products and reactants are present
C) only products are present
D) reactants predominate
E) products predominate
7) Which of the following expressions is the correct equilibrium-constant expression for the
reaction below?
2SO2 (g) + O 2 (g)
7)
2SO 3 (g)
A) [SO 3] / [SO2][O 2]
B) [SO 3]2 / [SO 2]2[O2]
C) [SO 3] / [SO2][O 2]2
D) [SO 3]2 / [SO 2]2[O2]2
E) [SO 2] / [SO3]
8) Which one of the following will change the value of an equilibrium constant?
A) varying the initial concentrations of reactants
B) changing temperature
C) varying the initial concentrations of products
D) adding other substances that do not react with any of the species involved in the
equilibrium
E) changing the volume of the reaction vessel
8)
9) The equilibrium-constant expression depends on the __________ of the reaction.
A) stoichiometry and mechanism
B) the quantities of reactants and products initially present
C) mechanism
D) stoichiometry
E) temperature
9)
2
10) The value of Keq for the following reaction is 0.25:
SO2 (g) + NO2 (g)
10)
SO3 (g) + NO (g)
The value of Keq at the same temperature for the reaction below is __________.
2SO2 (g) + 2NO2 (g)
A) 0.25
B) 0.12
2SO3 (g) + 2NO (g)
C) 0.50
D) 16
E) 0.063
11) A reaction vessel is charged with hydrogen iodide, which partially decomposes to molecular
hydrogen and iodine:
2HI (g)
H2(g) + I2(g)
When the system comes to equilibrium at 425 °C, PHI = 0.708 atm, and PH2 = PI2 = 0.0960 atm.
The value of Kp at this temperature is __________.
A) 6.80 × 10 -2
B) 1.30 × 10 -2
C) 1.84 × 10 -2
D) 54.3
E) Kp cannot be calculated for this gas reaction when the volume of the reaction vessel is not
given.
3
11)
12) At 900.0 K, the equilibrium constant (Kp) for the following reaction is 0.345.
2SO2 + O2 (g) → 2SO3 (g)
At equilibrium, the partial pressure of SO2 is 35.0 atm and that of O2 is 15.9 atm. The partial
pressure of SO3 is __________ atm.
A) 40.2
B) 82.0
C) 4.21 × 10-3
D) 6.20 × 10 -4
E) 192
4
12)
SHORT ANSWER (4 Points Each). Write the word or phrase that best completes each statement or answers the
question.
13) At elevated temperatures, molecular hydrogen and molecular bromine react to partially
form hydrogen bromide:
H2 (g) + Br2 (g)
2HBr (g)
A mixture of 0.682 mol of H2 and 0.440 mol of Br2 is combined in a reaction vessel with
a volume of 2.00 L. At equilibrium at 700 K, there are 0.556 mol of H2 present. At
equilibrium, there are __________ mol of Br2 present in the reaction vessel.
5
13)
14) Given the following reaction at equilibrium, if Kp = 0.990 at 250.0 °C, and the initial
pressure of PCl5 (g) is 2.5 atm. What is the partial pressure of Cl2 at equilibrium?
PCl5 (g)
PCl3 (g) + Cl2 (g)
6
14)