Science
Gibbs free energy.
Definition
Gibbs free energy (G) is a thermodynamic quantity that predicts whether a chemical reaction or process will occur spontaneously at constant temperature and pressure. A negative ΔG means the reaction is spontaneous (favorable), while a positive ΔG means it is non-spontaneous.
Examples
Real-world.
- 1 The combustion of glucose has a large negative ΔG, making it a spontaneous energy-releasing process
- 2 Ice melting above 0°C is spontaneous (ΔG < 0) because the entropy increase outweighs the enthalpy input
- 3 Photosynthesis has a positive ΔG and requires continuous energy input from sunlight to proceed
Key Fact
ΔG = ΔH − TΔS; if ΔG < 0, the reaction is spontaneous; if ΔG = 0, the system is at equilibrium.