The effects of chemical reaction on transient MHD free convection and mass transfer flow of dissipative fluid past an infinite vertical porous isothermal plate in the presence of heat generation, thermal diffusion and viscous dissipation is studied numerically. The Problem is governed by a coupled nonlinear system of partial differential equations. This system is solved numerically by applying explicit finite difference method. The effect of chemical reaction parameter (K) in the presence of Heat generation parameter (H) and Soret number (S₀) is examined on Velocity, Temperature and Concentration. The numerical values of the skin friction, the rate of heat transfer and the rate of mass transfer are entered in tables. It is found that chemical reaction parameter K decreases velocity and concentration in the presence or no presence of Heat source parameter H and Soret number S₀. Further, it has no effect on temperature.