# Can gibbs free energy be negative?

Sep 26, 2014

Yes, the Gibbs free energy can be negative or positive or zero.

All reactions are in principle equilibria.

If the position of equilibrium lies far to the right, we say that the reaction goes to completion. We then write the equation with a single arrow (→).

If the position of equilibrium lies far to the left, we say that there is no reaction.

The Gibbs free energy is related to the position of equilibrium.

ΔG = RTln(Q/K)

The sign of ΔG tells us the direction in which the reaction will shift to reach equilibrium.

If ΔG = 0, $Q = K$, and the system is at equilibrium.

If ΔG is negative, $Q < K$. The system spontaneously reacts to increase $Q$ (form more products).

If ΔG is positive, $Q > K$. The reaction will spontaneously go to the left. It will go to the right only if we provide an external stress (pressure, temperature, etc.) to make it go to the right.