7.6 They are both equal to 0.05 M.
7.7 [B]/[C] = 10 and [B] + [C] = 0.1 M
10[C] + [C] = 11[C] = 0.1 M → [C] = 0.009 M and [B] = 0.09
7.8 (a)
(b)
= −(2.0 M
−1 s
−1
)(0.1 M)(0.1 M) = −0.02 Ms
−1
= −(2.0 M
−1 s
−1
)(0.1 M)(0.1 M) = −0.02 Ms
−1
= (2.0 M
−1 s
−1
)(0.1 M)(0.1 M) − (1.0 s
−1
)(0.1 M)
+ (5.0 s
−1
)(0.1 M) = 0.42 Ms
−1
= (1.0 s
−1
)(0.1 M) − (5.0 s
−1
)(0.1 M) = −0.40 Ms
−1
(c) At equilibrium the concentrations of A and B are zero since the
reactions are irreversible. The sum of the concentrations must
be equal to 0.4 M and the ratio of the amounts of C and D is
given by the ratio of the two rate constants:
[C] + [D] = [C] + 0.2[C] = 0.4 M → [C] = 1/3 M
[D] = 0.2[C] = 1/15 M
7.9
7.10 (a)
(b)
(c) Since the reaction is irreversible, the final concentration of A is
zero and that of B is 0.2 M.
d B
d
A
s
M
Ms
[ ]
[ ] (
)( .
)
.
t
k f
= +
=
=
−
−
1
01
01
1
1
d A
d
A
s
M
M s
[ ]
[ ]
(
)( .
)
.
t
k f
= −
= −
= −
−
−
1
01
01
1
1
d A
d
A
d B
d
A
[ ]
[ ]
[ ]
[ ]
t
k
t
k
f
f
= −
= +
A A e
e
k
kt
k s
.
ln .
( )
=
→
=
=−
−
−
0
10
0 5
0 5
10
M
o r
s
.
=
−
0 0693
1
s
K
k
k
f
b
[ ]
[ ]
.
[ ]
. [ ]
=
=
=
→
=
D
C
D
C and
2
2
0 2
0 2
[ [ ] [ ]
.
C
D
M
+
= 0 4
d D
d
[ ]
t
d C
d
[ ]
t
d B
d
[ ]
t
d A
d
[ ]
t
d C
d
A B
C
D
d D
d
[ ]
[ ][ ]
[ ]
[ ]
[ ]
t
k
k
k
t
f
f
b
=
−
+
1
2
2
= =
−
[ ]
[ ]
k
k
f
b
2
2
C
D
d A
d
A B
d B
d
A B
[ ]
[ ][ ]
[ ]
[ ][ ]
t
k
t
k
f
f
= −
= −
1
1
450
ANSWERS TO PROBLEMS
9781405124362_5_end.qxd 4/29/08 9:17 Page 450