What does Gibbs free energy tell you?
Whether a reaction happens on its own. Negative ΔG = spontaneous; positive = needs an energy push; zero = at equilibrium. It is the master test for the direction of change.
// chemistry › Thermodynamics
Gibbs Free Energy (ΔG)
Calculate ΔG = ΔH − TΔS to test if a reaction is spontaneous, with symbol legend and real-world examples.
Δ G = Δ H - TΔ S
A mind behind this: Josiah Willard Gibbs 1839–1903
Frequently asked questions
How do ΔH and ΔS compete?
Reactions are favoured by releasing energy (negative ΔH) and increasing disorder (positive ΔS). Temperature sets how much the disorder term counts.
Why does temperature flip some reactions?
Because the TΔS term grows with temperature. A reaction can be non-spontaneous when cold and spontaneous when hot - like ice melting above 0°C.
How does ΔG connect to batteries?
ΔG = −nFE: a negative ΔG means a positive voltage, a battery that works. ΔG is the energy available to do useful work.
How does the example come out spontaneous?
ΔG = −100 − (298)(0.1) = −129.8 kJ/mol. Both terms push it negative, so it is strongly spontaneous.