Question

Physical Chemistry 1

The following mechanics has been proposed for the thermal decomposition of gaseous NO₂Cl

K₁

NO₂Cl = NO₂  + Cl

K_-1

NO₂ + Cl = NO₂Cl

K₂

NO₂Cl + Cl = NO₂  + Cl₂

Identify the conditions under which the overall reaction will exhibit First Order Kinetics and Second Order Kinetics with respect to NO₂Cl.

Answer 1

From the above reactions it is clear that an equilibrium is there between equations 1 and 2. And this is feeding the second equation.

If the equilibrium is attained fast then it becomes the feeding into the rate determining step. And if the equilibrium is slow then it becomes the rate determining step.

To make the equilibrium fast the temperature must be increased. Under these conditions the rate equation becomes: Rate = k[NO2Cl]²
However to make the equilibrium slow the temperature should be kept low, and first step becomes the rate determining step: Rate = k[NO2Cl]¹