You and your lab partner are studying the rate of a reaction, A + B --> C. You m
ID: 886617 • Letter: Y
Question
You and your lab partner are studying the rate of a reaction, A + B --> C. You make measurements of the initial rate under the following conditions:
(a) Which of the following reactant concentrations could you use for experiment 3 in order to determine the rate law, assuming that the rate law is of the form, Rate = k [A]x [B]y? Choose all correct possibilities.
[A] = 3.6 and [B] = 2.0
[A] = 1.8 and [B] = 4.0
[A] = 9.0 and [B] = 2.0
[A] = 7.2 and [B] = 2.0
[A] = 1.8 and [B] = 6.0
[A] = 3.6 and [B] = 6.0
[A] = 3.6 and [B] = 4.0
[A] = 5.4 and [B] = 2.0
(b) For a reaction of the form, A + B + C --> Products, the following observations are made: tripling the concentration of A increases the rate by a factor of 3, doubling the concentration of B has no effect on the rate, and tripling the concentration of C increases the rate by a factor of 27. Select the correct rate law for this reaction from the choices below.
Rate = k[A][B][C]
Rate = k[A][C]
Rate = k[A]2 [C]
Rate = k[A][C]2
Rate = k[A]2 [C]2
Rate = k[A]3 [C]
Rate = k[A][C]3
(c) By what factor will the rate of the reaction described in part (b) above change if the concentrations of A, B, and C are all halved (reduced by a factor of 2)?
The rate will be the original rate multiplied by a factor of .
Explanation / Answer
Answer –
a)In this one we are given that [A] and [B] and in the table there is same concentration for [B] and the different for the [A] , so we can calculate the order with respect to A, but not for B.
For calculating the order with respect to B we need two values of [A] constant, so the third experiment like either [A] with 1.8 or 3.6, so for experiment 3 in order to determine the rate law, assuming that the rate law is of the form, Rate = k [A]x [B]y and the following are the possibilities –
[A] = 3.6 and [B] = 2.0
[A] = 1.8 and [B] = 4.0
[A] = 1.8 and [B] = 6.0
[A] = 3.6 and [B] = 6.0
[A] = 3.6 and [B] = 4.0
b) When tripling the concentration of A increases the rate by a factor of 3, doubling the concentration of B has no effect on the rate, and tripling the concentration of C increases the rate by a factor of 27 means the rate is depend on the A and C only and not on B.
When tripling the concentration of A increases the rate by a factor of 3 means order with respect to A is first order and when tripling the concentration of C increases the rate by a factor of 27 means order with respect to C is third order
So rate law is
Rate = k[A][C]3
c) When we halved the concentrations of A, B, and C in the above reaction then there rate gets decrease by half in terms of [A] there is no change with respect to [B] and with respect to [C] there is rate gets 1/3 y its original rate.
The rate will be the original rate multiplied by a factor of 1/6.
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