Gibbs free energy – when a reaction turns spontaneous

ChemistryEnergetics & ThermodynamicsAges 15–16

Whether a reaction proceeds spontaneously is decided by the sign of ΔG = ΔH − TΔS. Pick a reaction (limestone calcination, NH₃ synthesis, dissolving NH₄NO₃...) and drag the temperature slider to see where the ΔG(T) line crosses zero — that crossover temperature is where the reaction turns spontaneous, explaining why lime kilns must run above 800 °C.