ThermochemistryHard

Question

ΔH for the reaction 2C(s) + 3H2(g) → C2H6(g) is –20.24 kcal/mol. The bond energies (in kcal/mol) of C–C, C–H and H–H are 63, 85.6 and 102.6, respectively. The enthalpy of sublimation of C(s) is

Options

A.124.3 kcal/mol
B.185.3 kcal/mol
C.158.3 kcal/mol
D.211.5 kcal/mol

Solution

$- 20.24 = \left\lbrack 2 \times \Delta_{\text{sol}}H_{C(s)} + 3 \times 102.6 \right\rbrack - \lbrack 63 + 6 \times 85.6\rbrack$

$\therefore\Delta_{\text{sub}}H_{C(s)} = 124.28\text{ kcal/mol}$

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