# Is Gibbs energy negative?

May 28, 2017

The change in Gibbs free energy is used to define if a certain reaction takes place spontaneously. You can calculate the change in Gibbs free energy with:

$\Delta G = \Delta H - T \times \Delta S$

If you have

A negative free energy change
then you calculated the energy remainder, after the spontaneity of the process, that is free to use for other purposes.

A positive free energy change
then you calculated the minimum amount of energy needed to run the process spontaneously.

Remember:
$\Delta G < 0$ $\textcolor{b l u e}{\text{Spontaneous}}$
$\Delta G = 0$ $\textcolor{b l u e}{\text{Reversible}}$
$\Delta G > 0$ $\textcolor{b l u e}{\text{Not spontaneous}}$