Gibbs = 0

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

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

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

JennyCKim1J
Posts: 51
Joined: Fri Sep 29, 2017 7:04 am

Gibbs = 0

When is Gibbs free energy equal to zero?

For this question:

The entropy of vap of water is 109.0J/mol*K. What is the enthalpy of vap of water at its normal boiling point of 100 degree C?

Why do we set G equal to zero?

Nha Dang 2I
Posts: 53
Joined: Fri Sep 29, 2017 7:07 am

Re: Gibbs = 0

deltaG=0 when the reaction is at equilibrium, so for that problem, it's because it's at a phase change.

Matthew Lin 2C
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

Re: Gibbs = 0

Yes you set deltaG equal to 0 when the reaction is at equilibrium, and you do it in this case because H20 is changing from liquid to vapor and vapor to liquid at equal rates at 100 degrees C (its normal boiling point).