The sharp interface model is examined for isothermal gas-solid reactions following zero-order kinetics with respect to the gas phase and first-order kinetics with respect to the solid phase for spherical particles either shrinking or growing during reaction. It is shown that depending on the relative magnitudes of the governing parameters which include the volume expansion factor, Damkohler number, and mass Biot number, it is possible to have up to three successive transitions from one controlling regime (external mass transfer, product layer diffusion, or chemical kinetics) to another as the reaction evolves with time. This behavior gives rise to various gas concentration and solid conversion profiles. A classification of all the possible situations is made.