Question

From the following data, calculate the enthalpy changc for the combustion of cyclopropane at $298\, K$. The enthalpy of formation of $CO _{2}(g), H _{2} O (l)$ and propane $(g)$ are $-393.5$, $-285.8$ and $20.42\, kJ\, mol ^{-1}$ respectively. The enthalpy of isomerisation of cyclopropane to propene is $-33.0\, kJ\, mol ^{-1}$.

Answer 1

Given : Cyclopropane $\longrightarrow$ Propene $\left( C _{3} H _{6}\right) ; \Delta H=-33 \,kJ$
Propene $\left( C _{3} H _{6}\right)+\frac{9}{2} O _{2} \longrightarrow 3 CO _{2}(g)+3 H _{2} O (l)$
$\Delta H=-3(393.5+285.8)-20.42=-2058.32 \,kJ$
Adding :
Cyclopropane $+\frac{9}{2} O _{2}(g) \longrightarrow 3 CO _{2}(g)+3 H _{2}(g)$
$ \Delta H =H_{1}+H_{2} $
$=-33+(-2058.32) \,kJ $
$ \Delta H =-2091.32 \,kJ $