Given the initial rate data for the reaction being A + B + C --> D determine the rate expression for the reaction and the (k) rate constant. (The units of [A] [B] and [C] are all moles/liter and the units of IRR is moles/liter seconds). If the [A]=[B]=[C]=.30M, what would the IRR be? [A] [B] [C] IRR 0.20 0.10 0.40 .20 0.40 0.20 0.20 1.60 0.20 0.10 0.20 .20 0.20 0.20 0.20 .80

k = 100 mol⁻² L² s⁻¹, r= k[A][B]²

Explanation:

A + B + C --> D

[A] [B] [C] IRR

0.20 0.10 0.40 .20

0.40 0.20 0.20 1.60

0.20 0.10 0.20 .20

0.20 0.20 0.20 .80

Comparing the third and fourth reaction, the concentrations of A and C are constant. Doubling the concentration of B causes a change in the rate of the reaction by a factor of 4.

This means the rate of reaction is second order with respect to B.

Comparing reactions 2 and 3, the concentrations of B and C are constant. Halving the concentration of A causes a change in the rate of the reaction by a factor of 2.

This means the rate of reaction is first order with respect to A.

Comparing reactions 1 and 3, the concentrations of A and B are constant. Halving the concentration of A causes no change in the rate of the reaction.

This means the rate of reaction is zero order with respect to C.

The rate expression for this reaction is given as;

r = k [A]¹[B]²[C]⁰

r= k[A][B]²

In order to obtain the value of the rate constant, let's work with the first reaction.

r = 0.20

[A] = 0.20 [B] = 0.10

k = r / [A][B]²

k = 0.20 / (0.20)(0.10)²

k = 100 mol⁻² L² s⁻¹