lec09 - Biochemistry I Fall Term 2004 Lecture 9 Biochemical...

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1 Biochemistry I Fall Term, 2004 September 20, 2004 Lecture 9: Biochemical Energetics 1 Assigned reading in Campbell: Chapter 12.1-12.5. Key Terms: Spontaneous Endergonic Exergonic Equilibrium constant ( G°= -RTln K eq ) Free energy ( G = H - T S) Enthalpy ( H) Entropy ( S) d lnK/ d T = H/RT 2 Conformational entropy (S = RlnW) Links : ( I ) Review Quiz on Lecture 9 concepts 12.1 Energy and Change We want to relate the measured equilibrium constants of spontaneous reactions to the thermodynamic features of those reactions. 12.2 The Criterion for Spontaneity G < 0 Spontaneous, exergonic. G = 0 Equilibrium. G > 0 Nonspontaneous, endergonic. 12.3 Standard States and the Standard Free Energy Change Standard states are arbitrary, but are agreed upon to allow easy comparisons between experimental results. Chemists and biochemists have agreed to use these standard states: Concentration: 1.0 M Water: 1.0 Pressure: 1.0 atm Free energy changes under these standard state conditions are designated as G°. Relationship between free energy ( G) and the equilibrium constant: G = G° + RT ln [Products]/[Reactants]
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2 At equilibrium, G = 0, and 0 = G° + RT ln [Products]/[Reactants]; therefore, G° = -RT ln [Products]/[Reactants] Since these are equilibrium concentrations of products and reactants, we can write, G = G° + RT ln K eq . Rewritng this equation, we have: G° = -RT ln K eq Thus, K eq and G° are both measures of how favorable a reaction will be.
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