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Third Law of Thermodynamics. Third Law of Thermodynamics. No finite sequence of cyclic processes can succeed in cooling a body to absolute zero. Nernst Postulate (Weak Form). The entropy change associated with any condensed system undergoing a reversible isothermal process
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Third Law of Thermodynamics Third Law of Thermodynamics No finite sequence of cyclic processes can succeed in cooling a body to absolute zero. Nernst Postulate (Weak Form) The entropy change associated with any condensed system undergoing a reversible isothermal process approaches zero as temperature approaches 0 K, where condensed system refers to liquids and solids. Walther Nernst (1864 – 1941)
Nernst Postulate (Strong Form) The entropy of all perfectly crystalline substances is zero at absolute zero. Max Planck (1858-1947)
Entropy of Substances Tabulated Results Function of Molecular Size Species So(298) J/K molSpecies So(298) J/K mol Li 29.1 HF 173.7 Na 51.4 HCl 186.8 K 64.7 HBr 198.6 Rb 69.5 HI 206.3 Cs 85.2 Function of Molecular Complexity Species So(298) J/K molSpecies So(298) J/K mol NO 211 CH4 186 NO2 246 C2H6 230 N2O4 304 C3H8 270 C4H10 310
Residual Entropy Ice I Structure Ice II Structure