Chem 1036
Test 2
Feb. 29, 2008
THIS IS FORM A
[FORM #s in ( )]
Name _________________________
K
w
= 1.0 x 10
-14
Choose the single best answer to each question.
1.(5)
The equilibrium constant,
K
c
, for the decomposition of COBr
2
COBr
2
(
g
)
CO(
g
) + Br
2
(
g
)
is 0.190. What is
K
c
for the following reaction?
2CO(
g
) + 2Br
2
(
g
)
2COBr
2
(
g
)
1.
0.0361
2.
2.63
3.
5.62
4.
10.5
5.
27.7
Answer:
5.
27.7
The second reaction is a result of reversing the first reaction and multiplying the
coefficients by 2 .
Reciprocal rule
:
reversing a reaction results in the new K value being the
reciprocal of the first reaction:
1
K
5.263
0.190
=
=
Coefficient rule:
multiplying a reaction by a factor n, like 2, results in the new K
value being equal to the first K value raised to the nth power.
So raise K to the 2
power: K = (5.263)
2
= 27.7
Or
2
1
K
0.190
⎛
⎞
=
⎜
⎟
⎝
⎠
= 27.7
2. (8)
The equilibrium constant,
K
p
, for the reaction
H
2
(
g
) + I
2
(
g
)
2HI(
g
)
is 55.2 at 425°C. A rigid cylinder at that temperature contains 0.127 atm
of hydrogen, 0.134 atm of iodine, and 1.055 atm of hydrogen iodide. Is the
system at equilibrium?
1.
Yes.
2.
No, the forward reaction must proceed to establish equilibrium.
3.
No, the reverse reaction must proceed to establish equilibrium.
4.
Need to know the volume of the container before deciding.

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