Equilibria and reactivities of quasi-chemical reactions

The structure elements of a sohd whose proportions vary according to different parameters are regarded as components of a solution. In other words, a sohd can be viewed as a solid solution of its stracture elements. 

This property allows us to apply all the properties of the components of a solution to structure elements. The mass action law of chemical equilibria especially applies to quasi-chemical equilibria using concentrations of structure elements. 

For the previous reaction of the oxygen vacancy with the gas, the mass action law for diluted defects will be written as follows at equilibrium  

The concentration of [Oo] in very high in the magnesium oxide and so is regarded to be constant, such as water molecules for ionic reactions in aqueous solution. This oxygen belongs to the solvent as well as the magnesium ions in normal cationic positions and the empty interstitial positions. 

Similarly, the reactivities of elementary quasi-chemieal reactions will be written as a function of the concentrations of the structure elements, through the rate coefficients. So, if the previous reaction was elementary (which is unlikely because it involves a fraction of atom), its reactivity would be  

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