The heat of combustion of ethylalcohol (C2H5OH) is 1380.7 kJ mol-1. If

1.	The heat of combustion of ethylalcohol (C2H5OH) is 1380.7 kJ mol-1. If the heats of formation of CO2 and H2O are 394.5 and 286.6 kJ mol-1 respectively. Calculate the heat of formation of ethyl alcohol.
Answer» (i) C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O ΔH = -1380.7 kJ (ii) C + O₂ → CO₂, ΔH = -394.5 kJ (iii) H₂ + \(\frac{1}{2}\)O₂ → H₂O, ΔH = -286.6 kJ We aim at 2C + 2H₂ + \(\frac{1}{2}\)O₂ → C₂H₅OH In order to get this thermochemical equation, multiply Eq. (ii) by 2 and Eq. (iii) by 3 and subtract Eq. (i) from their sum 2C + 3H₂ + \(\frac{1}{2}\)O₂ → C₂H₅OH ΔH = 2(-394.5) + 3(-286.6) - (-1380.7) = -268.1 kJ Thus the heat of formation of ethyl alcohol is ΔH_f = -268.1 kJ mol^-1

The heat of combustion of ethylalcohol (C2H5OH) is 1380.7 kJ mol-1. If the heats of formation of CO2 and H2O are 394.5 and 286.6 kJ mol-1 respectively. Calculate the heat of formation of ethyl alcohol.

Answer»

(i) C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

ΔH = -1380.7 kJ

(ii) C + O₂ → CO₂, ΔH = -394.5 kJ

(iii) H₂ + \(\frac{1}{2}\)O₂ → H₂O, ΔH = -286.6 kJ

We aim at 2C + 2H₂ + \(\frac{1}{2}\)O₂ → C₂H₅OH

In order to get this thermochemical equation, multiply Eq. (ii) by 2 and Eq. (iii) by 3 and subtract Eq. (i) from their sum

2C + 3H₂ + \(\frac{1}{2}\)O₂ → C₂H₅OH

ΔH = 2(-394.5) + 3(-286.6) - (-1380.7)

= -268.1 kJ

Thus the heat of formation of ethyl alcohol is

ΔH_f = -268.1 kJ mol^-1

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The heat of combustion of ethylalcohol (C2H5OH) is 1380.7 kJ mol-1. If the heats of formation of CO2 and H2O are 394.5 and 286.6 kJ mol-1 respectively. Calculate the heat of formation of ethyl alcohol.

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