Practice Questions Section 2.2
The Equilibrium Constant
Answers
Write balanced chemical equations for each of the following. Pay close attention to the physical states!
Also you must include the charge when writing ions, otherwise your answer is incorrect.
-
Do not balance these equations using fractions for coefficients.
sulfur dioxide gas combines with oxygen gas to produce sulfur trioxide gas
2 SO
2
2 SO
3 (g)
02
+
carbon monoxide gas burns in gaseous oxygen to produce carbon dioxide gas
2 CO
() +
2 CO2(g)
O2()
hydrogen chloride gas is produced from hydrogen gas and chlorine gas.
H
(
2
g) + Cl2(g)4* 2 HC1
nitrogen gas and oxygen gas combine to produce gaseous dinitrogen oxide.
2
2
N
g)
*—*
2N
0
2
(g)
solid hydrogen cyanide dissolves to produce hydrogen ions and cyanide ions in solution,
HCN(s)
(aq)
1
+
CN(aq)
solid silver chloride dissolves to produce silver ions and chloride ions in solution.
AgCI(S)
Ag
+
Cl(aq)
calcium ions and phosphate ions come out of solution to produce solid calcium phosphate.
3 Ca
2.
+
24
PO
(
3
aq)
4
(
3
Ca
2
)
P0
(s)
For each of the above reactions, write the equilibrium expression. Keq. for the reaction. Remember not to
include solids or liquids in the equilibrium constant expression.
2
2 SO3()
’(g)
50
[S03J
Keq
[503 110,1
2
[COJ
2CO(,)+O()2C0m)
Keq=
2
H2(g)+Cl2(g
H
Cl(g)
)
Kcq=[}
-
-
-
[CO ][Oj
[HCI]
]
2
[Cl
Keq=
2
[NO]
,
3
1
2
[N
]
[O
3
HCN(s)
H(aq)
+
CN(aq)
Keq
=
[H ][CN
I
)
5
AgCI(
Ag
+
Cl(aq)
Keq
=
[Ag ][Cl
I
3 Ca
+
23
PO4
(
aq)
Keq
4
(
3
Ca
2
)
P0 (s)
=
3.
j2
4
[
]
2
[Ca
3
PO
The equilibrium equation for the formation of ammonia is
2
N
+
2 NH
3 (g)
2
3 H
At 200°C the concentrations of nitrogen, hydrogen, and ammonia at equilibrium are measured and found to
be:
]
2
[N
=
2.12
]
2
[H
=
1.75
]
3
[NH
=
84.3
Calculate Keq at this temperature.
Solution:
K eq
4.
(84.3)2
2
]
3
[NH
=
] [H
2
[N
2
=
j3
(2. 12)(l
3
7.11x10
75)i
=
(2. 12)(5.36)
=626
answer
For each of the following equilibrium systems. identify whether the reactants or products are favored at
equilibrium, or whether they are equally favored.
Answer
COCl
(
2
e
C(S) +
Kcq
=
8.2x 102 at 627°C
reactants: 2
COCl
(
)
CH
(
4
g)
Keq
=
8.lx 108 at 25°
products; 4
CH
(
g)
Keq
=
2.24 at 227°C
equal
1.8 x
products: HCI(g)
2 H2(g)
5
PCI
3
PCI
H2(g) +
C(S)
CO ÷ 2
Cl
(
C)
Cl2(g)
1120
()
)
5
(
2
Mg(OH)
+
2>
Cl
2 HCI(g)
CO()
+
Mg
Keq
2
H
+
2 OH(aq)
—
Keq
=
Keq
—
at 25°C
I .96 at 1 000°C
1.2x
10h1
at 25°C
equal
reactants; Mg(OH)
)
5
(
2
4
5.
For the reaction: carbon monoxide bums in oxygen to produce carbon dioxide
You are given the following equilibrium conditions:
[021
1.30
l0
]
2
[CU
2.50
x
10
Keq
=
3.60
l0’
Calculate [CU]
Solution:
Begin by writing a balanced equation for the reaction:
2 CO(g) + O2(g)
2 CO
2 (g)
Next, set up the equilibrium constant expression and solve for the unknown, [CU]. You will find it easier
to let [CU] = x while you rearrange the equation:
K eq=
=
2
[CO,]
[CU]
[
2
0,]
3
3.60x10
=
2
)
4
(2.50x10
()
(
2
1.30x10)
3
(3.60x
)
(1.30x10
10
2
)
3
)
(x
=
8
(4.68x
)
6
)
2
=6.25x
(
10
l0
=
0.0134
=[CU]=0.116 M
2
)
4
(2.50x10