STOICHIOMETRY AND EXTENT OF DECOMPOSITION

The experimental stages in the study of a decomposition of a solid are as follows. Some or all of these stages may be omitted depending on the facilities available and the overall objectives of the work, though such omissions necessarily restrict the value and reliability of the conclusions obtained  

In the following Chapters (3 to 6), the main features of these stages are outlined and examples are given of studies which illustrate the successfiil use of appropriate experimental techniques, together with the necessary background theory. Applications of these principles and techniques are described in later Chapters (7 to 17), where the decompositions of specific groups of compounds are discussed in greater detail. 

The conventional method of measuring the amount of decomposition which has taken place is by the dimensionless fractional decomposition, a, which ranges from 0.00 for the pure reactant, to 1.00 signifying complete decomposition. On the assumption that both solid and gaseous products maintain a constant composition, a at any time during the decomposition may be measured directly from  

A technique, developed by Rouquerol [1] and known as constant rate thermogravimetry requires more sophisticated controllers to adjust the furnace temperature in such a way as to maintain a constant preselected value of do/dt over the major portion of the reaction. This increased complexity of the apparatus results in a simplification in the data treatment. 

Probably the most widely used methods of reactant preparation are by crystallization, or by precipitation fi-om solution. Sometimes use can be made of a silica-gel crystal growth technique [2], especially when the compound formed is a sparingly-soluble precipitate from aqueous solution. 

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