Calculate the enthalpy of combustion of ethylene at 300K at constant pressure if its enthalpy of combustion at constant volume is -"1406 kJ mol"^(-1).

Calculate the enthalpy of combustion of ethylene at 300K at constant p

1.	Calculate the enthalpy of combustion of ethylene at 300K at constant pressure if its enthalpy of combustion at constant volume is -"1406 kJ mol"^(-1).
Answer» Solution :The complete ethylene combustion reaction can be written as, `C_(2)H_(4(g))+3O_(2(g))rarr 2CO_(2(g))+2H_(2)O_((l))` `DeltaH=DELTAE+RT Deltan_((g))`, where `Deltan_((g))=n_(p(g))-nP_(r(g))`. `therefore""Deltan_((g))=2-(3+1)=-2`. Enthalpy of combustion at constant VOLUME `=DeltaE=-"1406 kJ mol"^(-1)` `therefore` Overall enthalpy of combustion `=DeltaH_(c)=-1406+(-2xx8.134xx10^(-3)xx300)` `=-1406-4.9884` `DeltaH_(c )=-1410.9kJ mol^(-1)`.