Tutorial 10 Notes - Nov 27th Dec 1st Tutorial Notes 1 a...

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Nov. 27 th , Dec 1 st Tutorial Notes 1) a) What is the standard Gibbs energy in both the biochemical and chemical convention for the reduction of pyruvate by NADH at 298K? (Reaction on page 162 of course notes.) H + + O O O - HO O O N O NH 2 N O NH 2 pyruvate lactate NADH NAD + H H Given that: NAD + + 2 e - + H + NADH E = -0.320 V pyruvate + 2 e - + 2 H + lactate E = -0.185 V Solution: We have been given the half-cell potentials for this reaction in the biochemical standard state so we can calculate the full cell potential using: E ! = E ! (right) " E ! (left) = " 0.185 + 0.320 V =0.135 V which can then be used to calculate standard biochemical Gibbs energy: ! G m " = # vFE " = # 2 96485 C mol -1 ( ) 0.135 V ( ) = # 26050 J mol -1 = # 26 kJ mol -1 To convert into the standard chemical Gibbs energy: ! G m " = ! G m o # 7 v H+ RT ln10 ! G m o = ! G m " + 7 v H+ RT ln10 Since the overall reaction has one molar equivalent of H+ as the reactant, v H+ = -1 : ! G m o = " 26.05 J mol -1 + 7 " 1 ( ) 8.314 J K -1 mol -1 ( ) 298 K ( ) ln10 # 10 " 3 kJ J -1 = " 65.98 kJ mol -1
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Therefore the change in Gibbs energy relative to the chemical standard state predicts that the reaction will be even more favorable than it is relative to the biochemical standard state. \ b) If [lactate] =2 mM, [pyruvate] = 50 mM, [NADH] = 2 mM, [NAD+]=0.504 M and pH = 7.4, what is the Gibbs energy? (Assume ideal solution behavior.) ! G m = ! G m " + RT ln Q " We need to find Q ! = a lactate a NAD+ a H + a pyruvate a NADH = b lactate b o " # $ % b NAD+ b o " # $ % b H + b ! " # $ % b pyruvate b o " # $ % b NADH b o " # $ % Note that we don’t have any mean activity coefficients as we were told that this is an ideal solution. We will be putting concentrations into units of mol/L so that b o can be eliminated from this equation: Q ! =
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This note was uploaded on 01/22/2011 for the course CHM 2132 taught by Professor Giorgi during the Fall '08 term at University of Ottawa.

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Tutorial 10 Notes - Nov 27th Dec 1st Tutorial Notes 1 a...

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