Chemistry / Unit 11 Chem 2096 short lesson, about 20 seconds
Standard Molar Entropy as an Absolute Quantity
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The idea
A substance's standard molar entropy, S°, is absolute, measured from the third law's zero-entropy point, unlike enthalpy of formation, always a difference relative to elements.
In practice
S° for a pure element is a nonzero, tabulated number, while ΔH°f for that element is exactly zero.
Where people slip
Reading S° and ΔH°f as parallel measures overlooks that only one has a true zero to measure from.
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