Gibbs free energy

The change in Gibbs free energy is the part of the enthalpy change of a reaction that is used to do work on the surrounding. In other words, $\Delta G$ is the maximum amount of work a reaction can do on the surroundings, i.e. $\Delta G=w_{max}$. If $\Delta G>0$, then the surrounding must do work on system.

The value of change in Gibbs free energy ($\Delta G$) for a certain reaction indicates whether a reaction is product favored ($\Delta G<0$) or reactant favored ($\Delta G>0$).

$\Delta G$ under known non-standard conditions can be calculated from standard values: $\Delta G=\Delta G^{\circ }+RT\ln K$ (mnemonic: AGAHSTAS), where $\Delta G^{\circ }$ is the standard Gibbs free energy change, $R$ is the ideal gas constant ($8.314\mathrm{J}/\mathrm{mol}\cdot \mathrm{K}$), and $T$ is the temperature.