AbstractA finite‐difference solution for unsteady free‐convection flow, taking into account mass‐transfer effects, is presented here. The concentrations of species, such as H, He, H2O, NH3, CO2are considered. The transient velocity, the transient temperature and the transient concentration profiles are shown on graphs. Also, the average and local Nusselt number, Sherwood number and skin‐friction are shown on graphs. The effects ofGr(Grashoff number) andSc(Schmidt number) for a fixed value ofN(buoyancy ratio parameter) are discussed. The stability and convergence of the implicit finite‐difference scheme are also es