Question

1. Suppose the following reaction takes place: 2A+B+C----->products. The following observations are made: Halving the ]A] halves the rate of reaction, trippling the [B] has no effect f the rate of reaction, and tripling [C] increases the rate of reaction nine-fold. What is the overall order of the reaction?

Please explain in clear details, thank you!

Answer 1

Given reaction is

2 A + B + C --- > Product

Lets show rate law for this reaction.

Rate = k [ A]^l[B]^m[C]ⁿ

Here k is rate constant and l, m and n are orders of A , B and C respectively.

Overall order of reaction = l+ m+ n

Lets find individual order.

From observation we say that if we half the concentration of A then order also becomes half. This means that the order with respect to A is 1 or l = 1, since order is raised to the power of the concentration and when there is linear change in order of the reaction then the order must be 1.

In second observation, after tripling the concentration of B there is no effect on the rate of the reaction.

We know Any number if raised to power 0 has answer =1 so there is no any change in rate from B and the order with respect to B is zero.

And m = 0

Now after tripling concentration of C order increase to the 9 fold.

That happens only if the value of n is 2

Since 3^2 = 9

So the order with respect to C is 2 nd

And n = 2

Lets find overall order

Overall order = l + m + n

= 1+0+2 = 3

So the given reaction is third order reaction.