A + B → C, If the concentration of A doubles, the rate of the reaction doubles.

Question

For a reaction, 

A + B → C, 

If the concentration of A doubles, the rate of the reaction doubles. While if the concentration of B doubles the rate of the reaction increases by four fold. Write rate law.

Answer 1

Let x moles of A react with y moles of B.

xA + yB → C

To write rate law, 

It is necessary to find x and y values.

(i) Initial rate

Final rate R₂ is doubled when the concentration of A is doubled, i.e., R₂ = 2R₁ when final concentration,

(It is assumed that the concentration of B remains same.)

(ii) Initial rate

If the concentration of B is doubled keeping of A constant, rate becomes four times, i.e.,

Hence,

The rate law is represented by an expression.

Rate = k[A] [B]²

∴ Rate law is Rate = k[A] [B]²