## Finding Gibbs Free Energy - 9.55 and 9.57

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

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

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

Athena Dong 2A
Posts: 11
Joined: Sat Jul 09, 2016 3:00 am

### Finding Gibbs Free Energy - 9.55 and 9.57

I noticed that there are two methods in the solutions manual for calculating the Gibbs free energy of a reaction:

1) $\Delta G =\sum \mathit{n}\Delta G_{f}(prod) - \sum \mathit{n}\Delta G_{f}°(reac)$
2) $\Delta G = \Delta H - T\Delta S$

They seem interchangeable for problems 9.55 and 9.57, but is one method more preferable over the other?

Thanks~

Tyler_Ash_3C
Posts: 25
Joined: Wed Sep 21, 2016 2:57 pm
Been upvoted: 1 time

### Re: Finding Gibbs Free Energy - 9.55 and 9.57

The two methods are interchangeable under standard conditions using the values given in Appendix 2A. Neither method is really preferable, but rather it depends on what information you are given in the problem or how the problem is asked. In instances under non-standard conditions, I think the second method would usually be preferable because you will probably be able to calculate entropy and enthalpy from the information given in the problem whereas you must be given the values of delta G for the products and reactants under non-standard conditions. But again, it just depends on what information you are given in the problem.