At 25ºC the standard enthalpies of formation of glucose and lactic acid are –127

Question

At 25ºC the standard enthalpies of formation of glucose and lactic acid are –1274 and –694.0 kJ mol-1, respectively. The heat capacities per mole of the two compounds are 218.7 and 127.6 JK-1 mol-1 at the same temperature.

(A) What is the enthalpy of reaction at 25ºC for the formation of lactic acid from glucose? The reaction is C6H12O6(s) 2CH3CHOHCOOH(s) (lactic acid).

(B) Assuming that the heat capacities given are independent of temperature, estimate Hº for the above reaction at the physiological temperature of 37ºC .

Explanation / Answer

A. Hf(Glucose) = -1274 kJ/mol; Hf(Lactic acid) = -694kJ/mol

Hreaction =Hf(Lactic acid) - Hf(Glucose)

                    = -694 -(-1274)

Hreaction = 580 kJ/mol

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