Gibbs energy and reversible work

When an ideal gas is reyersib y coiTfi constant te the work done 

During this isothermal process there is no change in internal energy, since the internal energy of an ideal gas is a function of temperature only, not a function of pressure or volume  

It follows from the first law that the heat absorbed by the system is the negative of the work done on the system  

The entropy change (numerically a decrease since Vi V2) is therefore 

There is no change in enthalpy, since enthalpy (like the internal energy) is for an ideal gas a function only of temperature  

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