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Chemistry 6440 / 7440

Chemistry 6440 / 7440. Thermochemistry. Resources. McQuarrie, Statistical Thermodynamics, University Science Books, 1973 Foresman and Frisch, Exploring Chemistry with Electronic Structure Methods, Chapter 4 Cramer, Chapter 10 Jensen, Chapter 12 www.gaussian.com/thermo.html.

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Chemistry 6440 / 7440

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  1. Chemistry 6440 / 7440 Thermochemistry

  2. Resources • McQuarrie, Statistical Thermodynamics, University Science Books, 1973 • Foresman and Frisch, Exploring Chemistry with Electronic Structure Methods, Chapter 4 • Cramer, Chapter 10 • Jensen, Chapter 12 • www.gaussian.com/thermo.html

  3. Thermodynamic Functions • U(T) - internal energy at absolute temperature T • H(T) = U(T) + PV = U(T) + RT - enthalpy • S(T) - entropy • G(T) = H(T) – T S(T) – free energy

  4. Thermodynamic Functions • at absolute zero, T = 0 U(0) = H(0) = G(0) U(0) = electronic energy + zero point energy S(0) = 0 for a pure crystalline substance (third law of thermodynamics)

  5. Thermodynamic Functions at T  0 • U(T) = U(0) + CvdT • heat at constant volume, molecule gains energy for translation (3/2 RT), rotation (3/2 RT) and vibration ( 1/(1-exp(-i/kT)) • H(T) = H(0) + CpdT • heat at constant pressure, molecule gains additional energy from expansion • S(T) > 0 • more states become accessible as the temperature increases

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