At 298 K, the bond dissociation enthalpies of C-C and C=C are 330 and 540 kJ/mol respectively. If the enthalpy of polymerisation per mole of polyethene [( C 2 H 4 ) n ( g )] from ethene gas at 2

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At 298 K, the bond dissociation enthalpies of C-C and C=C are 330 and 540 kJ/mol respectively. If the enthalpy of polymerisation per mole of polyethene [( C 2 ​ H 4 ​ ) n ​ ( g )] from ethene gas at 298 K is -6 MJ, find n .

TestHub · Accepted Answer

In the long-chain approximation, each ethene unit replaces one C=C bond with two C-C bonds. ΔH=n[540-2(330)]=-120n kJ mol⁻¹. The stated -6 MJ mol⁻¹ is -6000 kJ mol⁻¹, giving n=6000/120=50, B. End-group contributions are neglected as intended; an exact finite chain would require its termination to be specified.

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