It is statistically unlikely that any reac
tion requiring the simultaneous collision of
3 or more molecules will occur frequently
enough to contribute to the rate of the re
action.
Termolecular and higher moleculari
ties would happen so infrequently that there
would not be measurable rate of reaction.
020
4.0points
The reaction
N
2
+ 3 H
2
→
2 NH
3
is proceeding under conditions that 0.150
moles of NH
3
are being formed every 20 sec
onds.
What is the rate of disappearance of
H
2
?
1.
The question cannot be answered from
the information given; we need to know the
volume of the container.
Explanation:
n
NH
3
= 0.150 mol
t
= 20 s
The rate of appearance of NH
3
is
Rate =
1
2
Δ[NH
3
]
Δ
t
We can consider this to be
Rate =
1
2
·
0
.
150 mol
20 s
= 0
.
00375 mol
/
s
The rate of disappearance of H
2
is
Rate =

1
3
·
Δ[H
2
]
Δ
t
0
.
00375 mol
/
s =

1
3
·
Δ[H
2
]
Δ
t
Version 114 – Exam 3  S17 – labrake – (50355)
8
Δ[H
2
]
Δ
t
=

0
.
01125 mol
/
s
Thus H
2
disappears at a rate of 1
.
125
×
10
−
2
mol/s.
021
3.0points
If Substance A is a catalyst, which equation
best represents what happens in a chemical
reaction?
→
Which reaction has the larger rate con
stant?
023
3.0points
Consider the concentrationtime dependence
graph for two firstorder reactions.
2
= 0
.
097 M
−
1
s
−
1
T
1
= 326
.
85
◦
C + 273
.
15 = 600 K
[A]
0
Molar Concentration
of Reactant
Concentration
→
Time
→
Which reaction has the larger rate con
stant?
C. What is the activation energy
of this reaction?
k
2
= 0
.
097 M
−
1
s
−
1
T
1
= 326
.
85
◦
C + 273
.
15 = 600 K
Version 114 – Exam 3  S17 – labrake – (50355)
9
2
y
=
64
16
= 4 = 2
2
025
4.0points
The following data were collected for the re
action
2 A + B
2
+ C
→
D
Initial
Initial
Initial
Initial
[A]
[B
2
]
[C]
rate
(M)
(M)
(M)
(M/s)
1
0
.
01
0
.
01
0
.
01
1
.
250
×
10
3
2
0
.
02
0
.
01
0
.
01
5
.
000
×
10
3
3
0
.
03
0
.
01
0
.
05
1
.
125
×
10
4
4
0
.
04
0
.
02
0
.
01
8
.
000
×
10
4
Find the rate law.
1.
Rate = (1
.
25
×
10
7
) [A]
2
[B
2
]
2
2.
Rate = (1
.
25
×
10
9
) [A]
2
[B
2
]
3.
Rate = (1
.
25
×
10
11
) [A]
2
[B
2
]
2
correct
4.
Rate = (1
.
25
×
10
7
) [A] [B
2
] [C]
2
5.
Rate = (1
.
25
×
10
9
) [A] [B
2
]
2
y
= 2
Rate
3
Rate
1
=
k
[A]
2
3
[B
2
]
y
3
[C]
z
3
k
[A]
2
1
[B
2
]