## Dependence of free energy on pressure

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

JennyCKim1J
Posts: 51
Joined: Fri Sep 29, 2017 7:04 am

### Dependence of free energy on pressure

I don't really understand the equation for G. Is it G = free energy of the gas at 1 atm + free energy difference due to different pressure? Also, is the G just simple G or deltaG?

Victoria Draper 1G
Posts: 52
Joined: Fri Sep 29, 2017 7:05 am
Been upvoted: 1 time

### Re: Dependence of free energy on pressure

When the equation states "G = free energy of the gas at 1 atm + free energy difference due to different pressure" it is just verbalizing the equation of G=G°+RTln(P). If the RTln(P) part of the equation involves a pressure less than 1, then the whole value will be negative and will be subtracted from the value of free energy at the standard state. When the pressure is greater than 1 atm, the value of RTln(P) will be positive and will be added to the standard state. The whole equation shows how free energy depends on pressure and therefore should be noted as G rather than deltaG.

Sally Nason - 1K
Posts: 40
Joined: Fri Sep 29, 2017 7:05 am

### Re: Dependence of free energy on pressure

I was also confused by this in class but in the equation G = G^o + RTln(P/P^o), I believe that the P is the atmospheric pressure and the P^o is always 1.00 atm because it's standard. Therefore, when P is more than 1.00 atm, (P/P^o) is positive and when P is less than 1.00 atm, (P/P^o) is negative.