## Gibbs free energy

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

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

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

deniise_garciia
Posts: 30
Joined: Wed Nov 16, 2016 3:04 am

### Gibbs free energy

How can you tell when deltaG (Gibbs free energy) is spontaneous or non spontaneous?

Cynthia Aragon 1B
Posts: 47
Joined: Mon Apr 09, 2018 1:38 pm

### Re: Gibbs free energy

Delta G is spontaneous when Delta H and Delta S are positive at low or high temperatures. It's all spontaneous when Delta H is positive and Delta S is negative at all temperatures.

Delta G is nonspontaneous when Delta H is positive and Delta S is negative at all temperatures. It may also be nonspontaneous when Delta H and S are positive and either low or high temperatures.

Hope this helps.

Faith Fredlund 1H
Posts: 68
Joined: Fri Sep 28, 2018 12:18 am

### Re: Gibbs free energy

Also, in cases where ΔH is not positive and ΔS is not negative, but ΔS is still negative, you must look at the temperature of the reaction to determine if it is spontaneous or not because S is dependent of certain conditions including temperature.

Lorena Zhang 4E
Posts: 63
Joined: Fri Sep 28, 2018 12:16 am

### Re: Gibbs free energy

This is the gibbs free energy equation: deltaG = deltaH - TdeltaS
when deltaG is negative, the reaction is spontaneous; when it's positive, the reaction is non spontaneous.

Xinyi Zeng 4C
Posts: 63
Joined: Fri Sep 28, 2018 12:18 am

### Re: Gibbs free energy

Just to add on, you wouldn't really say if delta G is spontaneous or not.
The sign of delta G denotes whether the reaction/process is feasible or can take place spontaneously.

Parth Mungra
Posts: 72
Joined: Fri Sep 28, 2018 12:28 am

### Re: Gibbs free energy

You can look at the equation as well, dG=dH - TdS
If the entropy expression is greater than enthalpy, then the reaction will be spontaneous (exergonic), because dG is negative.

LilyL1C
Posts: 24
Joined: Fri Sep 28, 2018 12:20 am

### Re: Gibbs free energy

You can find Gibbs Free Energy by using the equation deltaG = deltaH - T(deltaS). And a reaction will be spontaneous if deltaG is a negative value, which can happen in three ways:
1. delta H is a small, positive number and delta S is a large positive number. This would give you
deltaG = positive# - T(positive#), which would result in a negative number.
2. delta H is a very large negative number and delta S is a very small negative number. This would give you
deltaG = negative# - T(negative#), which would result in a negative number.
3. delta H is a negative number and delta S is a positive number. This would give you
delta G = negative# - T(positive#), which would result in a negative number.
(Since temperature is always going to be a positive number, we don't have to worry about that affecting the signs of the equation. )

KHuang1L
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

### Re: Gibbs free energy

The reaction is spontaneous when delta G is negative and not spontaneous when delta G is positive.