Gibbs free energy (ΔG) directly tells us whether a reaction or process will happen on its own, which is what we call spontaneity. Here’s a explanation:
1. The rule
- ΔG < 0 → reaction is spontaneous (happens naturally).
- ΔG > 0 → reaction is non-spontaneous (won’t happen without energy input).
- ΔG = 0 → reaction is at equilibrium (no net change).
2. Why it works
- ΔG combines:
- Energy released or absorbed (enthalpy)
- Change in disorder (entropy)
- A reaction is spontaneous when the overall energy change favors the system (ΔG negative).
3. Everyday examples
- Ice melting at room temperature → ΔG is negative → happens spontaneously.
- Water freezing at room temperature → ΔG is positive → won’t happen spontaneously.
- Battery discharging → ΔG is negative → generates electricity spontaneously.
Summary
- Gibbs free energy is like a thermodynamic signal:
- Negative → go ahead, it happens on its own.
- Positive → needs energy input.
- Zero → system is balanced at equilibrium.