A general gas-solid reaction model is formulated. This work is the further development of the previous modelling work of Mazet (1988, Ph.D. Thesis, University of Perpignan) and Goetz (1991, Ph.D. Thesis, University of Perpignan) to simulate reversible gas-solid reactions that have been extensively applied to the new chemical heat pump technology developed at CNRS-IMP. In the present paper, a general coupled heat and mass transfer model has been developed and solved numerically. The global and local information yielded from this model are essential for a better knowledge of transfer mechanism concerning the significant influence of mass transfer in the pellet at low pressure and low permeability, important phenomena ignored by the previous models. Two reactive fronts in the transformation of the reactor have been found by this model, i.e. the "heat front" and the "mass front". Parameter sensitivity study from this model has classified the domain of influence of permeability and operating pressure on the global transformation of the reactor. This model has shown that when constraint pressure Pc > 4 bars and permeability k > 10(-13) m(2), previous models that consider heat transfer only at the global pellet level are still valid. In any other cases, the present model should be applied. Good agreement has been found between the simulation results of this model and the available analytical theory and experimental results for extreme boundary and initial conditions, and also for those within the practical experimental range. When a reactive material is given, this model can find out the pressure range in which this particular material can function correctly and efficiently. The simulation results from this model have also been compared with the recent experimental work of Prades (1992, Ph.D. Thesis, University of Perpignan) on a new material-IMPEX developed at CNRS-IMP. The comparison has confirmed the domain of influence yielded from this model and have indicated the variation of permeability during the reaction process. i