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- Sep 5, 2008
- Messages
- 511
- Reaction score
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Step 1 A→ B + C (slow)
Step 2 B + D → E + F (fast)
Step 3 E + C → G (fast)
In this case, the first step in the reaction pathway is the
rate-determining step. Therefore, the overall rate of the reaction
must equal the rate of the first step, k1[A] where k1 is the
rate constant for the first step. (Rate constants of the different
steps are denoted by kx, where x is the step number.)
In some cases, it is desirable to measure the rate of a
reaction in relation to only one species. In a second-order
reaction, for instance, a large excess of one species is
included in the reaction vessel. Since a relatively small
amount of this large concentration is reacted, we assume
that the concentration essentially remains unchanged.
Such a reaction is called a pseudo first-order reaction. A
new rate constant, k', is established, equal to the product of
the rate constant of the original reaction, k, and the concentration
of the species in excess. This approach is often
used to analyze enzyme activity
In a test of the rate of Step 3 of Reaction 1, a solution
is prepared containing a 0.1 M concentration of E and
a 50 M concentration of C. The rate is calculated after
the reaction has gone 50% to completion. By what
percent will the calculated rate differ from the true
rate if we treat the reaction as pseudo first-order?
A 0.02%
B. 0.05%
C. 0.1%
D. 0.2%
here is my approach
R = K (E) (C)
K(.1M *.5) (50-.5)---> K (.05)(49.95)--->2.4975K
R = K' (C)
K'(50*.5)----> k' (25)
The difference between the 2
k'(25)- k(2.4975) = 22.50k
22.50/2.4975=9
Step 2 B + D → E + F (fast)
Step 3 E + C → G (fast)
In this case, the first step in the reaction pathway is the
rate-determining step. Therefore, the overall rate of the reaction
must equal the rate of the first step, k1[A] where k1 is the
rate constant for the first step. (Rate constants of the different
steps are denoted by kx, where x is the step number.)
In some cases, it is desirable to measure the rate of a
reaction in relation to only one species. In a second-order
reaction, for instance, a large excess of one species is
included in the reaction vessel. Since a relatively small
amount of this large concentration is reacted, we assume
that the concentration essentially remains unchanged.
Such a reaction is called a pseudo first-order reaction. A
new rate constant, k', is established, equal to the product of
the rate constant of the original reaction, k, and the concentration
of the species in excess. This approach is often
used to analyze enzyme activity
In a test of the rate of Step 3 of Reaction 1, a solution
is prepared containing a 0.1 M concentration of E and
a 50 M concentration of C. The rate is calculated after
the reaction has gone 50% to completion. By what
percent will the calculated rate differ from the true
rate if we treat the reaction as pseudo first-order?
A 0.02%
B. 0.05%
C. 0.1%
D. 0.2%
here is my approach
R = K (E) (C)
K(.1M *.5) (50-.5)---> K (.05)(49.95)--->2.4975K
R = K' (C)
K'(50*.5)----> k' (25)
The difference between the 2
k'(25)- k(2.4975) = 22.50k
22.50/2.4975=9
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