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:

Experiment	[A] (M)	[B] (M)
1	1.9	0.9
2	3.8	0.9

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) [A] = 3.8 and [B] = 1.8

b)[A] = 1.9 and [B] = 2.7

c) [A] = 3.8 and [B] = 2.7

d) [A] = 5.7 and [B] = 0.9

e) [A] = 1.9 and [B] = 1.8

f) [A] = 3.8 and [B] = 0.9

g) [A] = 9.5 and [B] = 0.9

h) [A] = 7.6 and [B] = 0.9

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 3. Select the correct rate law for this reaction from the choices below.

a) Rate = k[A][B][C]

b) Rate = k[A][C]

c) Rate = k[A]²[C]

d) Rate = k[A][C]²

e) Rate = k[A]²[C]²

f) Rate = k[A]³[C]

g) 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 ____.

Answer 1

At the start, B is kept constant and A is doubled so, u get realation for rate of reaction and conc of A independent of B.

So find the dependence of rate of reaction on conc of B .. U need to keep the conc of A constant. That is , it may have values like 1.9 M and 3.8 M.

If A is 1.9 M then we consider exp-1 and exp-3 similarly, if A is 3.8 M then we consider exp-2 and exp-3.

At the same time we should not keep conc of B =0.9 since the again the conc of B will be same at all time

So,the possible options are

(a) ; (b) ; (c) and (e)

(2)

rate proportional to 1 st power of conc of A from statement-1

rate is independent of conc of B from statement -2

rate is proportional to 1 st power of conc of C from statement-3

So, b) Rate = k[A][C] is correct option

(3)

Rate = k[A][C]

new rate = k x[A/2][C/2]

=1/4 k[A][C]

=0.25 x original rate