The Effect of Temperature on Chemical Reaction Equilibrium

Source g° Isobutane (kcal/mol) °n-Butane (kcal/mol) iso normal (kcal/mol) 

We calculate the Gibbs energy change from liquid to hypothetical gas in three steps  

The liquid is reduced in pressure from the standard pressure of 1 bar to its vapor pressure at 298.15 K. 

The liquid is vaporized at that pressure, for which Ag = 0 because this is an equilibrium vaporization 

The vapor is replaced by an ideal gas, which will not condense, and compressed from the vapor pressure at 298.15 K to Ibar. 

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