The variation of Gibbs energy with temperature

To understand why phase transitions, inciuding the denaturation of a biopoiymer, occur at a specific temperature, we need to know how moiar Gibbs energy varies with temperature. 

For small changes in temperature, we show in the following Justification that the change in molar Gibbs energy at constant pressure may be written as 

This expression is valid provided the entropy of the substance is unchanged over the range of temperatures of interest. 

Justification 3.3 The variation of the Gibbs energy with temperature 

The starting point for this short derivation is eqn 3.2 in Justification 3.1, which we rewrite as the change in molar Gibbs energy when both the pressure and the temperature are changed by infinitesimal amounts  

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This method is based on Helmholtz s law, which specifies the variations of Gibbs energy with temperature ... 

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