Chem112 Day 19.docx - Chemistry 112 – Day 19 Back to the 2nd Law o Explain why ice melting is spontaneous o Explain why water freezing is spontaneous

Chem112 Day 19.docx - Chemistry 112 – Day 19 Back to the...

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Chemistry 112 – Day 19 (11/06/2019) Back to the 2 nd Law o Explain why ice melting is spontaneous o Explain why water freezing is spontaneous o What are we missing? o We must consider system and surroundings. o S univ = S sys + S suf Absolute Entropy (s) o In contrast to enthalpy we can get absolute values for S, not just S. o The third law tells us that a perfect crystal at absolute zero has 0 entropy. o How many microstates does this situation have? o We can look up standard molar entropies S Change in entropy from 0K to 298K J mol -1 K -1 Predicting Entropy Values o Physical States o Dissolving a solid or liquid Molecular solids Ionic solids o Dissolving a Gas A dissolved gas will always have a lower entropy value than the gas itself o Atomic Size and Molecular Complexity Larger size means more microstates Entropy increases with increasing complexity Problems o Which has the higher entropy of each pair?
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