# Calculate the enthalpy of formation of acetic acid if its anthalpy of combustion to CO2 and H2O is - 867 kJ/mol and the enthalpies of formation of CO2 and H2O are respectively - 393.5 and -285.9 kJ / mol ?

Nov 12, 2016

-491.8kJ/mol

#### Explanation:

Combustion reaction for above question is

${C}_{2} {H}_{4} {O}_{2} + 2 {O}_{2} \to 2 C {O}_{2} + 2 {H}_{2} O$

$\Delta {H}_{f} \left(c o m b u s t i o n\right) = 2 \left[\Delta {H}_{C {O}_{2}} + \Delta {H}_{{H}_{2} O}\right] - \Delta {H}_{{C}_{2} {H}_{4} {O}_{2}}$

$\Delta {H}_{{C}_{2} {H}_{4} {O}_{2}} = 2 \left[\Delta {H}_{C {O}_{2}} + \Delta {H}_{{H}_{2} O}\right] - \Delta {H}_{c o m b u s t i o n}$

$\Delta {H}_{{C}_{2} {H}_{4} {O}_{2}} = 867 + \left(2 \times - 679.4\right) = - 491.8 \frac{k J}{m o l}$