Delta G Units

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

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

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

Michele 2C
Posts: 23
Joined: Fri Sep 29, 2017 7:06 am

Delta G Units

So, I'm confused whether Gibbs free energy is reported in kJ or kJ/mole.
I know that molar Gibbs free energy implies kJ/mole. But standard Gibbs free energy is just reported in kJ (such as example 9.14, 9.15). But standard Gibbs free energy of formation is reported kJ/mole. Also, from 11.3, I know that the subscript 'r' also represents a molar quantity, so that would be reported in kJ/mole and the 'n' is just plugged in as a number (1 versus 1 mole). But how do we know in problems whether to use the molar quantity or not and whether to report Gibbs in kJ or kJ/mole? Is it okay to just always report it in kJ/mole?

Lily Guo 1D
Posts: 64
Joined: Fri Sep 29, 2017 7:03 am

Re: Delta G Units

The rule that I usually follow is to use kJ for standard delta G of a whole reaction because the products aren't necessarily only present in 1 mole. Therefore, you can't say that standard delta G of a reaction is necessarily going to be kJ/mole; all that "standard delta G" implies is that the reaction occurs under standard conditions. If it's delta G of formation, however, then I think that kJ/mole is generally used.