## Stability

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

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

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

Kyra Dingle 1B
Posts: 55
Joined: Fri Sep 29, 2017 7:04 am

### Stability

Why can we look at the Gibbs Free Energies of Formation to determine stability? Why would a positive free energy of formation indicate an unstable compound while negative ones indicate stable compounds?

Sohini Halder 1G
Posts: 58
Joined: Thu Jul 13, 2017 3:00 am
Been upvoted: 1 time

### Re: Stability

If Delta G for formation of a product A is negative, we know that the forward process is spontaneous and will "end up" as product A, meaning that product A is stable.
In the same vein, lets assume the Delta G for formation of product B is positive. The forward process that forms product B is not spontaneous, but the reverse reaction breaking down product B is. Therefore, B is unstable compound while A is stable.

Jana Sun 1I
Posts: 52
Joined: Sat Jul 22, 2017 3:00 am

### Re: Stability

Sohini Halder 1G wrote:If Delta G for formation of a product A is negative, we know that the forward process is spontaneous and will "end up" as product A, meaning that product A is stable.
In the same vein, lets assume the Delta G for formation of product B is positive. The forward process that forms product B is not spontaneous, but the reverse reaction breaking down product B is. Therefore, B is unstable compound while A is stable.

I think this concept comes up 9.63. I understand your logic Sohini, but the answer key for this problem says that, "Those compounds with a positive free energy of formation are unstable with respect to the elements." Are they trying to say that the reactants (aka the elements) for the compound are unstable? If so, it directly conflicts with what you're explaining.

However, following your logic (which I think makes more sense), if deltaG is positive, the reaction should proceed towards the reactant side, making the compounds with positive deltaG unstable with respect to...the compound itself, right? I'm just a little confused at how to interpret what the answers are saying.