Why standard entropy of an elementary substance is not zero whereas standard enthalpy of formation is taken as zero?
Why standard entropy of an elementary substance is not zero whereas standard enthalpy of formation is taken as zero?
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Entropy is zero only at absolute zero. Enthalpy of formation is the heat change involved in the formation of one mole of the substance from its elements. An element formed from itself means no heat change, i.e. ΔfH0 = 0.
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A substance has a perfectly ordered arrangement only at absolute zero. Hence, entropy is zero only at absolute zero. Enthalpy of formation is the heat change involved in the formation of one mole of the substance from its elements. An element formed from its constituents means no heat change.
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