7. Consider the following gas-phase equilibrium:
H
2
(g) + I
2
(g)
↔
2HI(g)
At a certain temperature, the equilibrium constant
K
c
is 4.0. Starting with equimolar
quantities of H
2
and I
2
and no HI, when equilibrium was established, 0.20 moles of HI
was present. How much H
2
was used to start the reaction?
a.
0.10 mol
b.
0.23 mol
c.
0.20 mol
d.
4.0 mol
e.
Need to know the volume of the reaction vessel.
8. At a certain temperature the equilibrium constant
K
p
= 0.132 for the reaction:
PCl
5
(g)
↔
PCl
3
(g) + Cl
2
(g)
At equilibrium, the partial pressures of both PCl
5
and PCl
3
are 100. mmHg. What is the
total pressure of the equilibrium system, in mmHg?
a.
100. mmHg
b.
200. mmHg
c.
300. mmHg
d.
400. mmHg
e.
332 mmHg
9. Ammonium iodide dissociates reversibly to ammonia and hydrogen iodide:
NH
4
I(s)
↔
NH
3
(g) + HI(g)
At 400ºC,
K
p
= 0.215. If 150 g of ammonium iodide is placed into a 3.00-L vessel and
heated to 400º C, calculate the partial pressure of ammonia when equilibrium is reached.
a.
0.22 atm
b.
0.46 atm
c.
0.11 atm
d.
0.88 atm
e.
1.2 atm
10. Consider the equilibrium reaction:
3CIO
-
(aq)
↔
CIO
3
-
(aq) + 2CI
-
(aq)
The equilibrium constant
K
c
= 3.2 X 10
3
. The following concentrations are present:
[Cl
-
] = 0.50 mol/L; [ClO
3
-
] = 0.32 mol/L; [ClO
-
] = 0.24 mol/L. Is the mixture at
equilibrium and, if not, in which direction will reaction proceed?
a.
The system is at equilibrium.
b.
The system is not at equilibrium; reaction will proceed left to right.
c.
The system is not at equilibrium; reaction will proceed right to left.
d.
The system cannot reach equilibrium since the ClO
3
-
and Cl
-
concentrations are
not in the stoichiometric ratio.
e.
There is not enough information to tell.
