Which type of reaction is always spontaneous?

Spontaneity is determined by the Gibbs free-energy change, ΔG = ΔH − TΔS. An exothermic reaction has ΔH < 0, and an increase in disorder means ΔS > 0, so both terms make ΔG negative at any temperature. Therefore, an exothermic reaction with an increase in disorder is always spontaneous.

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