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)

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)

TestHub · Accepted Answer

Per mole of 2-butyne, the C≡C bond becomes a C=C bond, and one new C–C bond links each monomer to the chain (the two methyl C–C bonds survive). The net change is: break one C≡C bond, form one C=C bond and one C–C bond. The enthalpy change is calculated as:

Δ H = 835 - 610 - 348 = -123 kJ

This corresponds to option (a).

Chemistry - Thermochemistry Question with Solution | TestHub

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