## Solving Gibbs Free Energy Problems

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

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

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

Jasmine 2C
Posts: 184
Joined: Wed Sep 18, 2019 12:18 am

### Solving Gibbs Free Energy Problems

For questions like 5G.15,
(a) Calculate the reaction Gibbs free energy of N2(g) + 3 H2(g) -> 2 NH3(g) when the partial pressures of N2, H2, and NH3 are 4.2 bar, 1.8 bar, and 21 bar, respectively, and the temperature is 400. K. For this reaction, K = 41 at 400. K. (b) Indicate whether this reaction mixture is likely to form reactants, is likely to form products, or is at equilibrium.
do we use the equation ΔGr = -RTlnK + RTlnQ only because K is given? If K isn't given, how would we solve this problem with ΔGr = ΔGr° + RTlnQ?

I feel like I forgot how to solve these problems after haven't done them in a while :(

Tyler Angtuaco 1G
Posts: 130
Joined: Wed Sep 11, 2019 12:16 am

### Re: Solving Gibbs Free Energy Problems

Yes, you can use the equation ∆G = ∆G° + RT ln Q since K is given. If K is not given, delta G naught or the equilibrium concentrations/pressures likely will be.