Lec-10-Chap13-2-bare

Lec-10-Chap13-2-bare - Lec-10-Chap13-2-bare 9/23/2011...

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Lec-10-Chap13-2-bare 9/23/2011 Directionality of Chemical Reactions Gibbs free energy. Calculations 1 Lec-10: Thermodynamics: Directionality of Chemical Reactions. Gibbs Free Energy Chapter 13 1 Wednesday, September 28, (in the first half of the lecture) Discussion about the course with Professor Troy Wolfskill Professor Fernando Raineri For a process at constant pressure   2 1 ext constant p T T P S C dT T P This equation allows us to calculate entropy changes (at constant pressure) by making calorimetric measurements. 2 initial initia final fi l l na SS From the definition of ∆S it follows that or, more explicitly       in final itial initial init final l l a fina i T T ST T T T C dT S
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Lec-10-Chap13-2-bare 9/23/2011 Directionality of Chemical Reactions Gibbs free energy. Calculations 2 Entropy: Thermodynamic Introduction The entropy of perfect crystals of all pure substances is zero at the absolute zero of temperature.         initial final 0 zero by 3rd Principle 00 0 absolute entropy 0K T T CT dT T S S T T S T S 3       in final itial initial init final l l a fina i T T ST T T T C dT S We can establish absolute entropies of substances with the help of the third principle of thermodynamics : 4     0 zero by 3rd Principle 11 0 absolute entrop 1 y 1 T T CC dT dT T S T  When the pressure is 1 bar (≈ 1 atm) we refer to the absolute entropy of 1 mol of substance as the standard molar entropy of the substance . 0 substance S In this way we can determine the absolute entropy of a pure substance at a given temperature T and pressure P . measured by calorimetry Tabulated at 25 °C
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Lec-10-Chap13-2-bare 9/23/2011 Directionality of Chemical Reactions Gibbs free energy. Calculations 3 Calculating Entropy Changes     0 , in reacta 0 nts 00 ,, reaction 0 reaction 0 , in products R f R R f P f P P f C D fB f A H c H d H aH H H H bH          0 in reactants 0 0 reaction 0 reac 0 in pro ti ducts o 0 n PP P C R R AB D R S cS d S S aS S S bS 5 We can then calculate enthalpy and entropy changes for reactions in standard conditions: C+ D+ A+ B+ ab cd Molecular Interpretation of the Entropy Internal energy: consists of the kinetic and potential energies of all molecules in the system. We recall the interpretations, at a molecular or microscopic level , of some of the thermodynamic quantities that we have encountered so far: Pressure: arises from the collisions of the molecules with the walls of the container.
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This note was uploaded on 03/06/2012 for the course CHE 132 taught by Professor Hanson during the Fall '08 term at SUNY Stony Brook.

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Lec-10-Chap13-2-bare - Lec-10-Chap13-2-bare 9/23/2011...

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