In the reaction: pyruvate + NADH + H + ⇌ lactate +...

Question

In the reaction: pyruvate + NADH + H + ⇌ lactate + NAD +: the standard reduction potentials of NAD+/NADH and private/lactate redox pairs are 0.32 V and -0.19 V respectively.a) Which redox pair has the greatest tendency to loose electrons (breifly explain)? Which is the stronger oxidizing agent (breifly explain)?b) If 1 M of each reactant and product are present at pH 7, which direction will the reaction proceed? why?c) Calculate ΔG° at 25°C and pH 7 for the reaction. Is the reaction spontaneous?

Jules Bruno · Accepted Answer

We’re being asked which of the given species has the greatest tendency to lose electrons and which is a stronger oxidizing agent. Species that lose electrons are reducing agents. Reducing agents are the species that are being oxidized in a redox reaction.Substances that gain electrons are oxidizing agents. The oxidizing agent is the species that are being reduced in a redox reaction. Recall the mnemonics LEORA GEROA.Lose              GainElectron         ElectronsOxidation       ReductionReducing      OxidizingAgent            AgentThe stronger reducing agent would be the species that would be easily oxidized or easily loses an electron:[readmore]• it will be the species that moves away from the electrons• it will be the anode which means it will have the lowest EcellThe stronger oxidizing agent would be the species that would be easily reduced or easily gains an electron:• it will be the species towards the electrons• it will be the cathode which means it will have the highest EcellThe ease to remove an electron from an element is also related to cell potential.• Smaller (↓) E°→ oxidation → stronger reducing agent → greater tendency to lose electrons• Larger (↑) E°→ reduction → stronger oxidizing agent → greater tendency to gain electronsReaction: pyruvate + NADH + H +⇌ lactate + NAD+Half reactions:Pyruvate + 2H+ + 2e- ⇌ Lactate     E°red = -0.19 V       ↑E°red → stronger oxidizing agent NAD+ + 2H+ + 2e- ⇌ NADH+ + H+  E°red = -0.32 V       ↓E°red → greater tendency to lose electronsPyruvate/Lactate pair is the stronger oxidizing agent because it has a larger E°red.NADH/NAD+ pair has a greater tendency to lose electrons because it has a smaller E°red.B. At pH 7 and 1 M of each product and reactant, calculate the cell potential:Oxidation:     Pyruvate + 2H+ + 2e- ⇌ Lactate              E°red = -0.19 V (cathode)Reduction:    NADH+ + H+ ⇌ NAD+ + 2H+ + 2e-             E°red = -0.32 V (anode)E°cell = E°cathode – E°anodeE°cell = -0.19 V – (-0.32 V)E°cell = 0.13 VThe positive E°cell indicates that the reaction moves in the forward direction.C. We’re asked to calculate the standard Gibbs Free energy. The cell potential of an electrochemical cell is related to Gibb's free energy of the reaction by the following equation:∆G° = Gibb’s Free Energyn = number of electrons transferredF = Faraday’s constant = 96485 C/(mol e-)E°cell =standard cell potentialFrom the half-reactions:Oxidation:     Pyruvate + 2H+ + 2e- ⇌ LactateReduction:    NADH+ + H+ ⇌ NAD+ + 2H+ + 2e-__________________________________________________________________Overall:         Pyruvate + NADH + H +⇌ Lactate + NAD+Two electrons are involved in the reaction, n = 2Solving for ∆G°***Recall: 1 CV = 1 J∆G°=-nFEcell°∆G°=-2 mol e-×96485 Cmol e-×0.13 V∆G° = 12545.05 CV∆G° = 12545.05 JThe negative value of ∆G° indicates that the reaction is spontaneous.

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