- 8

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i cant seem to figure them out.. and how would they be deduced?

i've come across one equation: Gf=Gi +nrtln(pf/pi) <- that i think may be for perfect gas. but i'm still unsure abotu the first expression.

thanks for any help.

- Thread starter koomanchoo
- Start date

- 8

- 0

i cant seem to figure them out.. and how would they be deduced?

i've come across one equation: Gf=Gi +nrtln(pf/pi) <- that i think may be for perfect gas. but i'm still unsure abotu the first expression.

thanks for any help.

- 55

- 0

dG= VdP-SdT

where V,P,S,T are volume, pressure, entropy and temperature, respectively. At constant T, above equation becomes

dG= VdP

For an ideal gas PV= nRT, then

dG= nRT dP/P

Integrating at constant T between Pi and Pf

Gf=Gi + nRT Ln ( Pf/Pi)

Where Gf and Gi are the Gibbs free energy at T and Pf , and at T and Pi, respectively. You can assume any value for Gi .

for a liquid you may use a convenient equation of state valid for the liquid phase. If the liquid is incomprensible V is almost independent of pressure, then

Gf=Gi + V(Pf-Pi)

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