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Temperature-Dependent Spontaneity and the Crossover Temperature

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State

For a reaction whose ΔH and ΔS share a sign, ΔG's sign depends on temperature, switching where ΔH equals TΔS exactly.

Show

A reaction with ΔH and ΔS both positive is nonspontaneous at low temperature but spontaneous past its crossover point.

Watch for

Calling a reaction "spontaneous" without stating the temperature ignores its own crossover.