Fundamental equation of chemical thermodynamics for gases.
We know already that the fundamental equation of chemical thermodynamics is
dG = VdP -SdT As we considered that the Temperature is constant we have come to this formula:
If you remember for solids and liquids we said that the volume was constant BUT the great difference between the solids/liquids and gases is that the volume in gases is not going to be constant so we use the ideal gas formula for 1 mol.
In the ideality for 1 mol of gas you can replace volumen like this:
Vi = RT/P
Therefore our new formule look like this:
Now if Pi= P° (Standard pressure @ 1 atm) Pf=P Therefore: Gf = G o + RT ln(P/ P°) Equation of molar gibbs energy of ideal gas.
Then you have to know that in REAL gases we replace P by the effective pressure called Fugacity (F).