Lec-16-Chap15-6-Complete

Lec-16-Chap15-6-Complete - Lec-16-Chap15-6-Complete...

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Lec-16-Chap15-6-Complete 10/12/2011 Chemical Equilibrium And Thermodynamics 1 Lec-16: Chemical Equilibrium Chapter 15 1 CHE 132 Second Midterm - Review Session: Friday October 14, 6:00 - 9:00 PM Harriman Hall 137 Directionality of Chemical Reactions Gibbs Free Energy Changes and Equilibrium Constants When discussing whether the product side of a reaction is favored or not (spontaneity of the reaction) , we have only considered the situation that both reactants and products are pure and in standard conditions. In such conditions we have concluded that: The sign of Δ G ° determines whether the products-side of the reaction is favored. spontaneous reaction at constant temperature and 1 bar pure reactants and pure pro 0 ducts G H T S p         2
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Lec-16-Chap15-6-Complete 10/12/2011 Chemical Equilibrium And Thermodynamics 2 Directionality of Chemical Reactions Gibbs Free Energy Changes and Equilibrium Constants However, in many cases, we need to decide whether a reaction will proceed spontaneously or not when the starting point involves mixed reactants (and maybe products) away from standard conditions. Even in such cases the Gibbs free energy G provides us with a criterion for deciding whether a reaction will occur spontaneously: Criterion for spontaneity provided by thermodynamics spontaneous reaction at constant temperature and pressure arbitrary initial conditions 0 G    3 Directionality of Chemical Reactions Gibbs Free Energy Changes and Equilibrium Constants But to be able to use this criterion we need to know how the Gibbs free energy change Δ G depends with the composition of the reaction system . Thermodynamics provides the answer: Criterion for spontaneity provided by thermodynamics spontaneous reaction at constant temperature and pressure arbitrary initial conditions 0 G Gibbs free energy change for the reac Gibbs free energy change for the re tion in standard conditi action in arb o Measures the deviation itrary condi from the ns st tions ln G RT G Q andard conditions 4
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Lec-16-Chap15-6-Complete 10/12/2011 Chemical Equilibrium And Thermodynamics 3 where the reaction quotient Q is defined as         (n Partial pressures of reactant and products at any conditio ot at equilibrium ns Concentrations of reactant and products at any con A0 B 0 0 C0 D0 0 0 ) dt 0 i + AB A CD D + C B ab c p c d cd PP Q d c Q  (not at equilibrium ions ) 5 Q p is used for reactions in gas phase or reactions involving gases and pure condensed phases. Q c is used for reactions in solution.
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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-16-Chap15-6-Complete - Lec-16-Chap15-6-Complete...

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