Gibbs free energy and Helmholtz energy
Chemical Thermodynamics · Chemistry
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For a reaction ΔH = −120 kJ, ΔS = −150 J/K. Find the temperature where it stops being spontaneous. Step 1: Set ΔG = 0: T = ΔH/ΔS. Step 2: T = (−120000)/(−150) = 800 K. Step 3: Below 800 K: ΔG < 0 (spontaneous); above: ΔG > 0. Step 4: Exothermic but disorder-decreasing — enthalpy wins at low T, entropy at high T. This is why ammonia synthesis runs hot but equilibrium prefers cold.