The polymerization of ethylene to linear polyethylene is represented by the reaction:<br><br>where h — Thermodynamics and Thermochemistry Chemistry Question
Question
The polymerization of ethylene to linear polyethylene is represented by the reaction:<br>$n\text{CH}_2=\text{CH}_2 \to (-\text{CH}_2-\text{CH}_2-)_n$<br>where $n$ has a large integral value. Given that the average enthalpies of bond dissociation for C=C and C–C at 298 K are +590 and +331 kJ/mol, respectively, the enthalpy of polymerization per mole of ethylene at 298 K is
💡 Solution & Explanation
In the polymerization process, for each monomer unit of ethylene, one $\text{C}=\text{C}$ double bond is broken (+590 kJ) and two $\text{C}-\text{C}$ single bonds are formed (since the double bond is converted to a single bond within the unit, and one new intermolecular single bond links to the next unit). $\Delta H = \text{BE(C=C)} - 2\text{BE(C-C)} = 590 - 2(331) = 590 - 662 = -72\text{ kJ/mol}$.