Absolute Entropy and Entropy Change
Every substance has a positive absolute (standard molar) entropy S° — and unlike formation enthalpy, elements have nonzero S°. A reaction's entropy change is computed the products-minus-reactants way: ΔS° = Σ S°(products) − Σ S°(reactants), each weighted by its coefficient.
The traps misjudge the magnitude of S° (a gas has much more than a solid; phase matters, not just particle count) and compute the sum wrong (missing coefficients, or reversing products and reactants). Weight by coefficients and subtract in the right order.
The work
3 ways in · any order
Lesson
Absolute Entropy
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Every substance (elements included) has a positive S°, and ΔS° = Σ products − Σ reactants with coefficients. The lesson computes entropy changes, then closes with a ten-scenario check.
Diagnostic
10-item topic check
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Ten items spanning the Topic 9.2 misconceptions: standard entropy magnitude misjudged (phase vs count), and the entropy sum computed with wrong coefficients or order.
Targeted Practice
Drill a single misconception
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Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.