ThermochemistryHard

Question

Enthalpies of combustion of CH4, C2H6 and C3H8 are −210, −370 and −526 kcal/mol, respectively. Enthalpy of combustion of hexane can be predicted as

Options

A.−840 kcal mol–1
B.−684 kcal mol–1
C.−1000 kcal mol–1
D.−500 kcal mol–1

Solution

Increase in |ΔcH| per unit increase in CH2 is $\frac{(370 - 210) + (526 - 370)}{2} = 158$

∴ Expected ΔcH of C6H14 = $( - 210) + 5 \times ( - 158)$= −1000 kcal/mol

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