2
$\begingroup$

Online I found the plot Gibbs free energy vs. reaction coordinate:

https://en.wikipedia.org/wiki/Transition_state_theory

and on many books I found the plot potential energy vs. reaction coordinate (e.g. page 237 Atkins, Physical Chemistry for the Life Sciences, 2nd Ed).

In the first case activation energy is defined as $\Delta G$, whereas in the second case is defined as difference of potential energy.

Thus is the Gibbs free energy a potential energy?

Thank you very much.

$\endgroup$
  • $\begingroup$ Gibbs free energy is defined for system/ensemble of particles. Potential energy surface is generally calculated to a single molecular complex. They are not in the same realm, but can estimated. $\endgroup$ – Greg Mar 13 '17 at 13:06
1
$\begingroup$

Yes both mean exactly the same thing.

By definition gibbs free energy is the total amount of non pv work that can be extracted from the system. Non Pressure-Volume work refers to the work which does not allow change in both volume and pressure of the system. An example of non pv work is electrical work which is done by cells and batteries in creating a potential difference about its ends.

Now pv work is related to kinetic energy of the molecules of the system. We can see this by two ways. First is that pressure and volume both are dependent on movement of molecules. Hence increasing pressure at constant volume is the same thing as increasing kinetic energy of the gas due to which there are more collisions of higher magnitude. Similarly increase in volume at constant pressure also means increase in kinetic energy of system. Second is that pressure and volume are both related and dependent on Temperature by gas equation where temperature of a system is directly related to kinetic energy of the gaseous system.

So whenever pv work is done by or on system changes take place only in kinetic energy of the molecules of system and not in the potential energy of system.

Hence whenever non pv work is done by or on system, changes in only potential energy of the system takes place. So Gibbs free energy is same as potential energy of system.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.