Here’s a explanation without any equations:
Gibbs Free Energy (G)
- Used when pressure and temperature stay constant.
- Tells us if a reaction or process can happen on its own.
- Shows how much useful work a reaction can do, like in chemical reactions or biological systems.
- Common in chemistry, biology, and open systems.
Helmholtz Free Energy (A or F)
- Used when volume and temperature stay constant.
- Also tells if a process can happen on its own.
- Shows the useful work a system can do in a closed, fixed-volume system.
- Common in physics, gases in rigid containers, and engineering studies.
Key Difference in Simple Terms
- Gibbs → Think “constant pressure” → like reactions in open containers.
- Helmholtz → Think “constant volume” → like reactions in a sealed box.
In short: Both tell if a process is spontaneous and how much work can be done, but Gibbs is for constant pressure, Helmholtz is for constant volume.