krohn (tek335) – H14: Kinetics 1 – Mccord – (52445)
1
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001
10.0 points
The rate of the reaction
2 O
3
→
3 O
2
is equal to
1.

1
3
Δ[O
2
]
Δ
t
.
2.

1
2
Δ[O
3
]
Δ
t
.
correct
3.

Δ[O
3
]
Δ
t
.
4.

Δ[O
2
]
Δ
t
.
5.
+
1
2
Δ[O
3
]
Δ
t
.
Explanation:
The rate of a chemical reaction can either
be expressed as the rate of disappearance of
a reactant (as in this case) or as the rate
of appearance of a product.
However, this
rate is multiplied by the inverse of the coef
ficient of the species in question.
The nega
tive sign here reminds us that as the reaction
progresses, this species is consumed and de
creases in concentration.
002
10.0 points
When the reaction
3 NO(g)
→
N
2
O(g) + NO
2
(g)
is proceeding under conditions such that 0.015
mol/L of N
2
O is being formed each second,
the rate of the overall reaction is
?
and
the rate of change for NO is
?
.
1.
0.015 M
·
s
−
1
; +0.045 M
·
s
−
1
2.
0.030 M
·
s
−
1
;

0.005 M
·
s
−
1
3.
0.015 M
·
s
−
1
;

0.005 M
·
s
−
1
4.
none of the other answers is correct
5.
0.015 M
·
s
−
1
;

0.045 M
·
s
−
1
correct
Explanation:
Notice that three moles of NO are required
to make one mole of N
2
O in this reaction,
so the rate of disappearance of NO (which
has a negative sign) is
three
times the rate of
appearance of N
2
O.
003
10.0 points
Consider the irreversible reaction
A + 2 B
→
3 C
.
Which of the following correctly expresses
the rate of change of [B] ?
1.
Δ[B]
Δ
t
=

1
2
(rate of rxn)
2.
Δ[B]
Δ
t
= +2 (rate of rxn)
3.
Δ[B]
Δ
t
=

(rate of rxn)
4.
Δ[B]
Δ
t
= +
1
2
(rate of rxn)
5.
Δ[B]
Δ
t
=

2 (rate of rxn)
correct
6.
Δ[B]
Δ
t
= +(rate of rxn)
Explanation:
As B is a reactant and consequently disap
pears during the reaction, its rate of change
will be negative and the inverse of the coeffi
cient is used when writing the rate:
(rate of rxn) =

1
2
Δ[B]
Δ
t

2 (rate of rxn) =
Δ[B]
Δ
t
004
10.0 points
Suppose a compound is involved in three
different reactions denoted
R
1
,
R
2
, and
R
3
.
Tripling the concentration of this reactant in
all three reactions causes the rates of reaction
to increase by factors of 3, 9, and 1, respec
tively. What is the order of each reaction with
respect to this reactant?
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krohn (tek335) – H14: Kinetics 1 – Mccord – (52445)
2
1.
R
1
= 0;
R
2
= 1;
R
3
= 2
2.
R
1
= 2;
R
2
= 0;
R
3
= 1
3.
R
1
= 3;
R
2
= 9;
R
3
= 1
4.
R
1
= 1;
R
2
= 2;
R
3
= 0
correct
5.
R
1
= 1;
R
2
= 3;
R
3
= 0
Explanation:
Tripling the concentration of the reactant
in
R
1
brings about a tripling (= 3
1
) increase
in the rate of the reaction, so the reaction is
first
order with respect to the reactant in this
case.
Likewise, tripling the concentration of the
reactant in
R
2
brings about a 9fold (= 3
2
)
increase in the rate of the reaction, so the
reaction is
second
order with respect to the
reactant here.
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 Spring '07
 Holcombe
 Kinetics, Chemical reaction, Rate equation, Krohn

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