ThermochemistryHard
Question
The enthalpy of formation of liquid methyl alcohol in kJ/mol, using the following data (in kJ/mol).
Heat of vaporization of liquid methyl alcohol = 38.
Heat of formation of gaseous atoms from the elements in their standard states: H, 218; C, 715; O, 249.
Average bond energies: C−H, 415; C−O, 356; O−H, 463.
Options
A.−190
B.−702
C.−626
D.−266
Solution
Required thermochemical equation is
$C(s) + 2H_{2}(g) + \frac{1}{2}O_{2}(g) \rightarrow CH_{3}OH(l)$
$\Delta H = \lbrack 715 + 4 \times 218 + 249\rbrack - \lbrack 3 \times 415 + 356 + 463\rbrack - 38 = - 266\text{ kJ}$
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