CHEM 1120 Edition 1nd Lecture 29 Outline of Last Lecture I Defining Entropy a Entropy as energy dispersal b Molecular Motion II Chemical Reactions and S Outline of Current Lecture I Chemical Reactions and S a 3rd Law of thermodynamics b Standard Molar entropies c 2nd Law II Gibbs Free Energy G a G H TS III Free Energy and Temperature IV Free Energy and the Equilibrium constant Current Lecture I II Chemical Reactions and S a 3rd Law of thermodynamics i Entropy of a pure crystalline substance at absolute zero is 0 ii Straight line when melting or boiling because more microstates exist b Standard Molar entropies i Pure substances must have a positive S ii For pure elements S does not 0 iii Generally S gas S liquid S solid iv Generally higher molar mass higher S v Generally more atoms in a molecule higher S vi S Sum of S products sum of S reactants c 2nd law for a spontaneous process S universe 0 i S universe S system S surroundings ii S surroundings q surroundings T q system T H rxn T V Gibbs Free Energy G a G H TS b If G is negative the forward reaction is spontaneous i 0 reaction at equilibrium These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III IV ii Is positive reverse reaction is spontaneous c Standard Free Energy Changes i Standard state pure liquids and solids gases at 1 atm solutions at 1 M for elements Gf 0 d G equals the maximum useful work that can be done by the system at constant T and P G w max Free Energy and Temperature a Does G 0 for spontaneity make sense Yes i Most spontaneous reactions are exothermic ii Spontaneous processes tend to have a positive S that is T S negative Free Energy and the Equilibrium constant a G G 0 RTlnQ b Reaction quotient Q the value of the equilibrium expression under any conditions c Thermodynamics of living systems i Many reactions needed for life are not spontaneous 1 Building tissue nerve signals muscle contraction oxygen transport 2 How Energy coupling spontaneous reaction drives nonspontaneous reaction 3
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