Initial rate analysis

Initial rate analysis for a reaction may be done to understand the mechanism of a reaction. Initial rate is defined as the rate at zero conversion. It is obtained by extrapolation of the rate vs conversion data to zero conversion. For higher accuracy, the conversion data are collected at very low conversion region. In this method, the dependence of initial rate data on partial pressure or total pressure of the reactant is studied.

Consider the reaction

The rate expression derived from Langmuir Hinshelwood model when surface reaction is controlling is

........................(2)

Now at zero conversion all the product concentration will tend to zero, hence putting
C_C =0 & C_D =0, the rate expression [2] simplifies to

.....................................................(3)

Where r_i is the initial rate. Now if a equimolal initial concentration of C_A and C_B is used then C_A= C_B. Then assuming ideal gas mixture, , where p_A is the partial pressure of A.

Similarly where p_B is the partial pressure of B .

Now since it is an equimolal mixture, then at initial condition. where p_t is the total pressure.

Or

Then substituting C_A and C_B in equation [3] becomes