Abstract: The guidelines for assessing the apparent activation energies of gas/solid reactions have been proposed based on the experimental results from literatures. In CO₂ free inlet gas flow, CaCO₃ decomposition between 950 and 1250 K with thin sample layer could be controlled by the interracial chemical reaction with apparent activation energy E = (215±10) kJ/mol and E = (200±10)kJ/mol at T = 813 to 1020 K, respectively. With relatively thick sample layer between 793 and 1273 K, the CaCO₃ decomposition could be controlled by one or more steps involving self-cooling, nucleation, intrinsic diffusion and heat transfer of gases, and E could vary between 147 and l90 kJ/mol. In CO₂ containing inlet gas flow (5%-100% of CO₂), E was determined to be varied from 949 to 2897 kJ/mol. For SrCO₃ and BaCO₃ decompositions controlled by the interfacial chemical reaction, E was (213±15) kJ/mol (1000-1350 K) and (305+15) kJ/mol (1260-1400 K), respectively.