An investigation of the effect of chemical reaction and thermal radiation on unsteady MHD free convection heat and mass transfer of an electrically conducting, viscous, incompressible and heat absorbing fluid flow past a vertical infinite flat plate embedded in a porous medium is carried out. The flow is induced by a general time-dependent movement of the vertical plate, and the cases of ramped temperature and isothermal plates are studied. Exact solution of the governing equations is obtained in closed form by Laplace transform technique. Expression for skin friction and Nusselt number are derived for both ramped temperature and isothermal plates. Some applications of practical interest are discussed for different types of plate motions. Expression for Sherwood number is also derived. The numerical values of fluid velocity, fluid temperature and species concentration are displayed graphically whereas the numerical values of skin friction, the Nusselt number and the Sherwood number are presented in tabular form for various values of pertinent flow parameters for both ramped temperature and isothermal plates. It is being found that the chemical reaction and thermal radiation parameter leads to decrease the fluid velocity for both ramped temperature and isothermal plate whereas the porosity parameter decreases the fluid velocity for both ramped temperature and isothermal plate throughout the boundary layer region. The radiation parameter increases the fluid temperature for ramped temperature but decreases in case of isothermal plate whereas chemical reaction parameter decreases the species concentration throughout the boundary layer region.

free convection, chemical reaction, thermal radiation, MHD, porous medium, ramped temperature.