ThermochemistryHard

Question

The bond enthalpies of C–C, C=C and C≡C bonds are 348, 610 and 835 kJ/mol, respectively at 298 K and 1 bar. The enthalpy of polymerization per mole of 2-Butyne at 298 K and 1 bar as shown below is

nCH3–C≡C–CH3(g) → –(CH2–CH=CH–CH2)n– (g)

Options

A.−123 kJ
B.−132 kJ
C.−139 kJ
D.−37 kJ

Solution

$\Delta H = \left( \text{B.E}\text{.}_{\pi\text{ bond in C=C}} \right) - \left( \text{B.E}\text{.}_{\sigma\text{ bond in C} - C} \right) = (835 - 610) - 348 = - 123\text{ kJ}$

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