Applications of standard affinities

The examples discussed in 3 and 4 show clearly the importance of tables of standard affinities and standard heats of formation, since from them we can calculate the thermodynamic behaviour of an almost unlimited number of reactions. 

Before going on in 7 to a detailed consideration of some particular reactions we may illustrate the use of these tables for rather more qualitative considerations. 

For example, if we wish to know qualitatively whether chlorine tends to displace iodine from its compounds we may take, as a typical reaction, 

We find, taking the standard affinities of formation of the molecules involved from table 8.1, and proceeding as in the last paragraph, that 

Clearly under these conditions the concentrations of HCl and 12 will be enormously large compared with those of HI and Cl 2 so that we can conclude that chlorine will displace iodine from hydrogen iodide. 

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