Relationship between enthalpy, entropy, and Gibbs






Moderators: Chem_Mod, Chem_Admin

Tam To 1B
Posts: 72
Joined: Fri Sep 28, 2018 12:25 am

Relationship between enthalpy, entropy, and Gibbs

Postby Tam To 1B » Tue Feb 19, 2019 11:03 am

How does free energy change with temperature when the value of enthalpy is negative and entropy is negative?
How does free energy change with temperature when the value of enthalpy is positive and entropy is positive?

Milena Aragon 2B
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

Re: Relationship between enthalpy, entropy, and Gibbs

Postby Milena Aragon 2B » Tue Feb 19, 2019 11:09 am

When both enthalpy and entropy are negative, the temperature has to be relatively low for Gibbs to be spontaneous (i.e. negative). When both enthalpy and entropy are positive, the temperature has to be relatively high for Gibbs to be spontaneous. If you look at the equation and plug in positive or negative values for each respective variable, it will make more sense why you need a high or low temp in order to obtain a negative Gibbs value.

Laura Gong 3H
Posts: 89
Joined: Fri Sep 28, 2018 12:26 am
Been upvoted: 1 time

Re: Relationship between enthalpy, entropy, and Gibbs

Postby Laura Gong 3H » Tue Feb 19, 2019 1:42 pm

When change in enthalpy and entropy are both negative, raising the temperature would make the change in free energy more positive. (less spontaneous)
When change in enthalpy and entropy are both positive, raising the temperature would make the change in free energy more negative. (more spontaneous)

Ethan Breaux 2F
Posts: 63
Joined: Sat Sep 29, 2018 12:16 am

Re: Relationship between enthalpy, entropy, and Gibbs

Postby Ethan Breaux 2F » Tue Feb 19, 2019 2:39 pm

delta G = delta H - T x delta S

Like someone above said if you plug in numbers to the equation it'll make pretty good sense.
Most of this stuff will be dependent on temperature.

varunhariharan
Posts: 30
Joined: Mon Jan 07, 2019 8:16 am

Re: Relationship between enthalpy, entropy, and Gibbs

Postby varunhariharan » Tue Feb 19, 2019 3:40 pm



In order for the reaction to be spontaneous, ΔG = -, so:
If ΔH = - , and ΔS = + , the reaction is spontaneous at any temperature.
If ΔH = - , and ΔS = - , the reaction is spontaneous at low temperature.
If ΔH = + , and ΔS = + , the reaction is spontaneous at high temperature.
If ΔH = + , and ΔS = - , the reaction is never spontaneous.


Return to “Gibbs Free Energy Concepts and Calculations”

Who is online

Users browsing this forum: No registered users and 2 guests