## Finding Spontaneity of Reaction

$\Delta U=q+w$

Jennifer Su 2L
Posts: 47
Joined: Wed Nov 21, 2018 12:20 am

### Finding Spontaneity of Reaction

Towards the end of lecture on Friday Week 4, Lavelle talked about how just knowing delta U (or delta H) isn't enough to know if a reaction will occur and that we also need to know the entropy (S). Can someone explain how knowing delta U and S will tell us how the system will change? In other words, what values of U and S will cause the reaction to be spontaneous, and what values would cause it to not be spontaneous?

Matthew Tran 1H
Posts: 165
Joined: Fri Sep 28, 2018 12:16 am

### Re: Finding Spontaneity of Reaction

The state function G (Gibb's free energy) allows us to determine the spontaneity of a reaction by the relation: $\Delta G^{\circ} = \Delta H^{\circ} - T\Delta S^{\circ}$. When $\Delta G^{\circ}$ is negative, the reaction is spontaneous, and when it's positive, the reaction is not spontaneous. I wouldn't expect this to be on the midterm though since it only goes up to the end of entropy.