Define enthalpy of combustion. Calculate the enthalpy of combustion of methanol if the enthalpies of formation of CO2,H20 andCH3OH are respectively . -393.5kj/mol,-285.8kj/mol and -239.0kj/mol.

Md Ariful Islam

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Answer: Enthalpy of combustion is the heat released during combustion of one mol amount of any substance by oxygen.

You can calculate the combustion enthalpy of methanol using the enthalpy of formation of all components involved in reaction.

Reaction involved:

2CH3OH + 3O2 = 2CO2 + 4H2O

For O2 enthalpy of formation is zero.

So enthalpy of combustion = ∆H(CO2) + ∆H(H2O) - ∆(MeOH) - ∆(O2)

= -393.5 - 285.8 + 239 + 0

= - 440.3 kj/mol

So enthalpy of combination of MeOH is - 440.3 kj/mol

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