Ch1b09Lecture14

Ch1b09Lecture14 - 1 MidTerm Review 7 p.m. Thursday evening...

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Unformatted text preview: 1 MidTerm Review 7 p.m. Thursday evening in here Midterm covers up to but not including the Carnot Cycle 2 A few comments on taking your midterm 3 Gibbs Free Energy Three state functions: E, H, S H (enthalpy) and S (entropy) are most important A fourth state function, G, connects both H and S together G = H TS G is the Gibbs Free Energy 4 Gibbs Free Energy G is the Gibbs Free Energy G sys > 0 G sys = 0 G sys < 0 Non-spontaneous process Reversible process Spontaneous process G = H -T S For chemical reactions at a constant temperature 5 Gibbs Free Energy This is just like the enthalpy ( H o ) discussion we had last time. 6 Gibbs Free Energy G = H -T S Entropy determines the temperature-dependence of G Gases exhibit the largest T dependence Followed by solutions Followed by solids Why is this? Think about the statistical definition of entropy. 7 Gibbs Free Energy & Chemical Equilibrium [ ] [ ] [ ] [ ] ln c d a b aA bB cC dD G R T K C D K A B + + = = [ ] [ ] [ ] [ ] ln c d a b aA bB cC dD G R T K C D K A B + + = = This is the equation that we want to get to 8 Gibbs Free Energy & Chemical Equilibrium haracteristics of Equilibrium States They display no macroscopic evidence of change They are reached through spontaneous processes They show a dynamic balance of forward and everse processes They are the same regardless of direction of pproach 9 Empirical Law of Mass Action aA + bB cC + dD Consider the following general reaction egardless of the initial conditions, the value of the ratio [ ] [ ] [ ] [ ] b eq a eq d eq c eq B A D C K = Remains constant! This is the law of mass action 10 Reaction Coordinates efore we apply the concepts of the law of mass action, lets over some of the basic issues related to how chemical eactions proceed We start with reaction coordinate diagrams 11 Reaction Coordinate Diagrams Reaction Coordinate reactants products E a E E a = energy of activation (not a state function) E = energy difference (usually G) between reactants and products (a state function) H + I 2 HI + I H---I---I transition state 12 Reaction Coordinate (distance) reactants products E a E H + I 2 HI + I H---I---I transition state licker question: If I knew E, then I could, using what I have learned to date in Chem 1B, calculate the amount of products and reactants at quilibrium. True False 13 Equilibrium and G o Reaction Coordinate reactants products G 1 G o A+B C+D transition state [ ] [ ] [ ] [ ] b eq a eq d eq c eq P B A D C K = Assume aA + bB cC + dD in the gas phase, then G -1 G o = Gibbs free energy difference between reactants & products G 1 = energy barrier separating reactants & products in the forward direction sort of like E a G -1 = energy barrier separating reactants & products in the reverse direction True or False G o 1 = G o-1 14 Equilibrium and G o [ ] [ ] [ ] [ ] b eq a eq d eq c eq B A D C K...
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Ch1b09Lecture14 - 1 MidTerm Review 7 p.m. Thursday evening...

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