Affinity as a function of temperature

We now calculate the affinity as a function of temperature in the general case by evaluating the integral in (4.10). 

From Kirchhoff s equation (2.32) we have first, (using the abbreviation = 

We see clearly that to calculate A at a given temperature T, pressure p, and extent of reaction we must know 

the affinity may be obtained for any given temperature, from a knowledge of its value at any one temperature by the use of purely calorimetric measurements The right hand side of (4.17) may be written in various alternative forms which are often useful. 

The double integral, which appears both in (4.17) and (4.19), may be transformed, by integration by parts to 

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