Thermodynamics and Thermochemistry 2 Question 18

18. From the following data, calculate the enthalpy change for the combustion of cyclopropane at 298 K. The enthalpy of formation of $\mathrm{CO}{2}(g), \mathrm{H}{2} \mathrm{O}(l)andpropane(g)are393.5,285.8and20.42 \mathrm{~kJ} \mathrm{~mol}^{-1}respectively.Theenthalpyofisomerisationofcyclopropanetopropeneis-33.0 \mathrm{~kJ} \mathrm{~mol}^{-1}$.

(1998, 5M)

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Solution:

  1. Given : Cyclopropane Propene $\left(\mathrm{C}{3} \mathrm{H}{6}\right) ; \Delta H=-33 \mathrm{~kJ}Propene\left(\mathrm{C}{3} \mathrm{H}{6}\right)+\frac{9}{2} \mathrm{O}{2} \longrightarrow 3 \mathrm{CO}{2}(g)+3 \mathrm{H}_{2} \mathrm{O}(l)$;

ΔH=3(393.5+285.8)20.42=2058.32 kJ

Adding :

Cyclopropane $+\frac{9}{2} \mathrm{O}{2}(g) \longrightarrow 3 \mathrm{CO}{2}(g)+3 \mathrm{H}_{2}(g) ;$

ΔH=H1+H2 =33+(2058.32)kJ ΔH=2091.32 kJ