1: Pyruvic acid is produced as the final product in the metabolism of glucose vi

Question

1: Pyruvic acid is produced as the final product in the metabolism of glucose via the glycolytic pathway. Prior to entry into the Krebs (i.e. the citric acid) cycle, pyruvate is oxidized to acetate. Consider the hypothetical oxidation reaction of pyruvic acid as following:

CH3COCOO (aq) + 12 O2(g) CH3COO (aq)+ CO2 (g)

Calculate the entropy change involved in the oxidation of pyruvic acid to acetic acid at T = 298 K as described in this reaction. You may use tabulated entropy of formation for CO2 and O2. [Hint: For pyruvate ion, S0f = 179.9 J K–1 mol–1, and for acetate ion, S0f =

113.0 J K–1 mol–1].

2: In the Krebs cycle, degradation of the carbon skeleton of glucose is completed when acetate ion is oxidized to carbon dioxide and water. The net reaction for the Krebs cycle is given by:

CH3COO– (aq) + H+ (aq) + 2O2(g) 2CO2(g) + 2H2O(l)

Calculate the entropy change for this reaction at T = 298 K. [Hint: You may use tabulated entropy of formation for each product and reactant appearing in this reaction. For acetate ion (CH3COO–), S0f = 113.0 J K–1 mol–1].

Explanation / Answer

1)   CH3COCOO (aq) + 1/2 O2(g) CH3COO (aq)+ CO2 (g)

S0f of CH3COCOO = 179.9 J K–1 mol–1,

S0f of CH3COO- = 113.0 J K–1 mol–1.

s0f OF o2 = 205.0 J K–1 mol–1.

s0f OF co2 = 213.6 J K–1 mol–1.

dsrxn = Sproducts - Sreactants

     = (113.0+213.6)-(179.9+(1/2)*205)

     = 44.2 J K–1 mol–1.

2) CH3COO– (aq) + H+ (aq) + 2O2(g) 2CO2(g) + 2H2O(l)

S0f of CH3COO- = 113.0 J K–1 mol–1.

s0f OF o2 = 205.0 J K–1 mol–1.

s0f OF co2 = 213.6 J K–1 mol–1.

s0f OF h2o = 69.9 J K–1 mol–1.

s0f OF H+ = 0.0 J K–1 mol–1.

dsrxn = (2*213.6+2*69.9)-(113.0+0.0+2*205.0)

       = 44 J K–1 mol–1.

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