The bond enthalpies of C-C, C=C and C≡C bonds are 350, 615 and 812 kJ/mol, respectively, at 298 K and 1 bar. The enthalpy of polymerization per mole of acetylene at 298 K and 1 bar, as shown below, is
nCH≡CH(g) → -(CH=CH)_n-(g)

Question

The bond enthalpies of C-C, C=C and C≡C bonds are 350, 615 and 812 kJ/mol, respectively, at 298 K and 1 bar. The enthalpy of polymerization per mole of acetylene at 298 K and 1 bar, as shown below, is

nCH≡CH(g) → -(CH=CH)_n-(g)

TestHub · Accepted Answer

Per mole of acetylene the C≡C bond becomes a C=C bond and one new C-C bond links each monomer to the chain (the C-H bonds are untouched). Net: break 1 C≡C, form 1 C=C + 1 C-C: ΔH = 812 - 615 - 350 = -153 kJ. This is option (b).

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