### Delta G spontaneity

Posted:

**Fri Feb 22, 2019 9:06 am**How can you tell if delta G is spontaneous or non spontaneous when it is Temperature dependent?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=135&t=42622

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Posted: **Fri Feb 22, 2019 9:06 am**

How can you tell if delta G is spontaneous or non spontaneous when it is Temperature dependent?

Posted: **Fri Feb 22, 2019 9:17 am**

When Delta G is given and you see the standard symbol it means standard temperature which is 298K. Also 1M and 1Atm is standard. Delta G is spontaneous when Delta H is positive and and Delta S is positive. Also, Delta G is spontaneous when both Delta H and Delta s are negative.

Delta G is non-spontaneous when both Delta H and Delta S are positive. Moreover, it can be that both Delta H and Delta S are negative.

Positive meaning favorable which increases entropy and negative meaning unfavorable which decreases entropy.

Delta G is non-spontaneous when both Delta H and Delta S are positive. Moreover, it can be that both Delta H and Delta S are negative.

Positive meaning favorable which increases entropy and negative meaning unfavorable which decreases entropy.

Posted: **Fri Feb 22, 2019 10:24 am**

As a side note, you can further solve for when it becomes spontaneous by setting the equation equal to zero and solving for T.

Posted: **Fri Feb 22, 2019 9:42 pm**

Here's a picture that may help.

Posted: **Fri Mar 15, 2019 6:27 pm**

When you plug in the temperature and other variables, as long as delta G is negative, then the reaction is spontaneous.

Posted: **Fri Mar 15, 2019 6:35 pm**

When delta H and delta S have differing signs then the reaction is temperature dependent

Posted: **Fri Mar 15, 2019 6:39 pm**

"Delta G is non-spontaneous when both Delta H and Delta S are positive. Moreover, it can be that both Delta H and Delta S are negative. " is not correct. It MAY become nonspontaneous

Posted: **Fri Mar 15, 2019 9:20 pm**

you really just have to look at delta G in relation to the other variables such as delta H, delta S, and T

knowing their signs will help you determine whether or not delta G is positive or negative, thus giving you spontaneity

knowing their signs will help you determine whether or not delta G is positive or negative, thus giving you spontaneity