Q.

From the following data, calculate the standard enthalpy change for the combustion of cyclopropane at 298 K:

The standard enthalpy of formation of CO2(g), H2O(l) and propene(g) are - 393.5, - 285.8 and 20.42 kJ mol-1 respectively.

The standard enthalpy of isomerization of cyclopropane to propene is -33.0 kJ mol-1.

Report your answer by rounding off to the nearest integer [magnitude only].


Ans.

(2091)

CH3CH=CH2(g)+92O2(g)→3CO2(g)+3H2O(l)

ΔcH(Propene)Θ=[3ΔfH(CO2)Θ+3ΔfH(H2O)Θ]-[ΔfH(Propene)Θ+92ΔfHO2Θ]

=3(-393.5)+3(-285.8)-(20.42)=-2058.32 kJ mol-1

To the above reaction, if we add the reaction:

∴   ΔcH(cyclopropane)Θ=(-2058.32-33.0) kJ mol-1=-2091.32 kJ mol-1