Gibbs free energy is a measure of the usable energy in a system that can do work at constant temperature and pressure.
- It tells us whether a chemical reaction or physical process can happen spontaneously.
- If the Gibbs free energy decreases (ΔG is negative), the process is spontaneous.
- If ΔG is positive, the process won’t happen on its own.
- If ΔG is zero, the system is at equilibrium, and no net change occurs.
Everyday example:
- Ice melting at room temperature: ΔG is negative → it happens spontaneously.
- Water freezing at room temperature: ΔG is positive → it doesn’t happen spontaneously.
In short, Gibbs free energy predicts spontaneity and how much useful energy is available from a reaction or process.