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An endothermic process is not spontaneous at the freezing point of water but turns spontaneous at the boiling point of water. Which statement about its thermodynamic quantities is correct?

1. ΔH is negative and ΔS is positive
2. Both ΔH and ΔS are positive
3. Both ΔH and ΔS are negative
4. ΔH is positive and ΔS is negative

Correct answer: Both ΔH and ΔS are positive

Solution

For an endothermic process delta H is positive. It is non-spontaneous at low T but spontaneous at high T, which from delta G = delta H - T*delta S requires delta S to be positive. Hence both delta H and delta S are positive.

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