Calculate the enthalpy change for the oxidation of pyruvic acid to acetic acid u

Question

Calculate the enthalpy change for the oxidation of pyruvic acid to acetic acid under standard conditions (298 K, 1 atm): The heats of combustion of pyruvic acid and acetic acid under standard conditions are -279 kcal/mol and -207 kcal/mol, respectively. Heats of combustion are determined by reacting pyruvic acid or acetic acid with O2 (g) to give H2O (l) and CO2 (g). As a first step, write balanced chemical equations for the combustion reactions for pyruvic acid and acetic acid, then combine them to make the overall reaction (above) for the oxidation of pyruvic acid to acetic acid.

Explanation / Answer

CH3COOH + 2O2 ----> 2CO2 + 2H2O ---- (combustion of acetic acid)

2C3H4O3 + 5O2 = 6CO2 + 4H2O -----> (combustion pf pyurvic acid)

Multiply first equation by 2 and reverse the equation we get the desired rxn

2CH3COCOOH + O2 ----> 2CH3COOH + 2CO2

Enthalpy Change = 2*(combustion of pyurvic acid) - 2*(combustion of acetic acid)

=> 2*(-279) + 2 * 205

=> 2 * (-72) => -144 Kcal/mol

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