Gibbs Free Energy

Gibbs free energy combines the enthalpy change and the entropy change, adjusted for temperature, to tell you whether a process is thermodynamically favorable at constant temperature and pressure. The idea is that a reaction is driven forward by releasing heat (negative ΔH) and by increasing disorder (positive ΔS), but the entropy term only matters strongly when multiplied by temperature. If ΔG is negative, the process can proceed spontaneously in the forward direction; if positive, the reverse direction is favored unless energy is supplied.

Use this formula when you need to judge whether a chemical reaction, phase change, or biochemical process is favorable under specific temperature conditions. It is especially useful in equilibrium chemistry, electrochemistry, and reactions where temperature changes can switch spontaneity.

• Forgetting to convert entropy units so that ΔS matches the energy units used for ΔH
• Using the sign of ΔG to predict speed instead of spontaneity; thermodynamics does not tell you reaction rate
• Assuming a reaction with negative ΔG is spontaneous in every condition, when temperature can change the result