The initial solid is not stoichiometric

We still assume that only one gas is released. A certain amount of this gas can leave the solid A without causing the decomposition reaction this amount is related to the pressure and temperature conditions. This case is encountered, for example, in the decomposition of the boehmite that maintains a significant distance from stoichiometry by water departure (see Chapter 16). It is thus advisable to determine as a preliminary the e amormt of gas likely to leave A rmder the conditions of the decomposition. This determination carmot be, in general, made during the decomposition because the latter very often starts before the stoichiometry of A is at equilibrium. On the other hand, we can determine the variations of s with pressure and temperature only under conditions that do not give place to the decomposition and then extrapolate the value of s in the conditions of the decomposition. 

We can make the same remark as we did in the preceding case after considering variations of s with operating conditions while studying the influence of these conditions on the decomposition. 

Remark.- If the initial solid A is non-stoichiometric and if the increase in this nonstoichiometry proceeds at the same time as that of the decomposition, it leads to a non-pseudo-steady state evolution since there is accumulation of the defects. 

Remark - The same problem arises if the A solid adsorbs a certain amount of a gas (of the reaction or not) this amount must be withdrawn from the initial mass for the calculation of the fractional extent. 

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