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Unformatted text preview: Name: TF Name: 1 LS1a Fall 08 Problem Set #2 Due Monday 10/6 at noon in your TF’s drop box on the 2 nd floor of the Science Center 1. Shown below is a free energy diagram for the reaction (a) (4 points) On the diagram, clearly label Δ G° rxn as well as the position of equilibrium on the x-axis. Also, indicate with arrows the direction in which the reaction will proceed spontaneously at the two points (1 and 2) highlighted on the curve. (b) Is Δ G° rxn for this reaction positive or negative? Is the reaction (as written) thermodynamically favorable or unfavorable under standard state conditions? (6 points) Δ G° rxn is positve because G for the products is greater than G for the reactants. Reactions with positive free energy differences are thermodynamically unfavorable. (c) What can you say about the magnitude of K eq for this reaction? (2 points) Since the reactants are favored over the products, K eq will be less than 1. (d) What is the sign (or the value) of Δ G° rxn at equilibrium? (6 points) Δ G° rxn is a constant based on standard state conditions and typically non-equilibrium values for reactant and product concentrations. Thus the value of Δ G° rxn will not change whether or not the reaction is at equilbrium. The sign of Δ G° rxn remains positive. (e) What is the sign (or the value) of Δ G at equilbrium? (2 points) At equilibrium, Δ G is equal to 0. A + B C + D Name: TF Name: 2 2. Humans metabolize consumed ethanol into Acetyl-CoA, which can then be used to generate cellular energy. This process occurs in multiple steps as shown below: Ethanol Acetaldehyde Acetic Acid Acetyl-CoA Energy The first reaction in the pathway and its ∆ G˚ rxn is shown below: Ethanol Acetaldehyde ! G˚ rxn = +47,200 J/mol (a) Based on the value of ∆ G˚ rxn , is the K eq for this reaction greater than 1, less than 1, or equal to 1 under standard state conditions? (2 points) K eq will be far less than one, indicating that the reactants are favored over the products. Whether or not this reaction can proceed towards the right under non-standard conditions depends on where the reaction lies with respect to equilibrium. (b) What do the magnitude of ∆ G at a particular state and the sign of ∆ G at a particular state tell us about the reaction at that particular state and its relative relationship to reaching equilibrium? (6 points) The sign of ∆ G at a particular state tells us the direction in which a reaction will proceed towards equilibrium. If the ∆ G at a particular state is less than zero (negative), then the reaction (as written) will proceed forward to equilibrium. If the ∆ G at a particular state is greater than zero (positive), the reaction will proceed backwards towards equilibrium (going forward is...
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This document was uploaded on 03/23/2011.
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