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Thermodynamics

# From the given data, calculate the enthalpy of combustion of cyclopropane at $298 \: K$. The enthalpy of formation of $CO_2(g), H_2O(l)$ and propene(g) are $-393.5, -285.8$ and $20.42 \: kJ/mol$ respectively. The enthalpy of isomerisation of cyclopropane to propene is $-33 \: kJ/mol$

$\begin {array} {1 1} (A)\; 2037.9\: kJ & \quad (B)\;-2091.32 \: kJ \\ (C)\;2091.32 \: kJ & \quad (D)\;- 2037.9 \: kJ \end {array}$

$C(s) + O_2(g) \rightarrow CO_2(g); \Delta H_1 = -393.5\: kJ$
$H_2(g) + \large\frac{1}{2}$$O_2(g) \rightarrow H_2O(l); \Delta H_2 = -285.8\: kJ$
$3C(s) + 3H_2(g) \rightarrow C_3H_6(g); \Delta H_3 = 20.42\: kJ$
$\Delta H = 3 \Delta H_1 + 3 \Delta H_2 - \Delta H_3 - \Delta H_4$
$= 3(-393.5) + 3(-285.8) – 20.42 – (-33) = -2091.32\: kJ$
Ans : (B)