The polymerisation of ethylene to linear polyethylene is represented by the reaction, .n[ CH 2= CH 2] longrightarrow -[ CH 2- CH 2]n- where, n has large integral value. Given that the average enthalpies of bond dissociation for C = C and C - C at 298 K are +590 and +311 kJ / mol respectively, calculate the enthalpy of polymerization per mole of ethylene at 298 K.

Question

The polymerisation of ethylene to linear polyethylene is represented by the reaction, .n[ CH 2= CH 2] longrightarrow -[ CH 2- CH 2]n- where, n has large integral value. Given that the average enthalpies of bond dissociation for C = C and C - C at 298 K are +590 and +311 kJ / mol respectively, calculate the enthalpy of polymerization per mole of ethylene at 298 K. (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

Per mole of ethylene polymerized, one C = C bond is broken and two C - C bonds are formed. Δ H° (Polym. )=590-2 × 311 =-32 kJ / mol

Per mole of ethylene polymerized, one C=C bond is broken and two C−C bonds are formed. ΔH∘ (Polym. )=590−2×311 =−32kJ/mol

Per mole of ethylene polymerized, one $C = C$ bond is broken and two $C - C$ bonds are formed.
$Δ H^{\circ}$ (Polym. $) = 590 - 2 \times 311$
$= - 32 k J / m o l$