Question

Calculate the enthalpy change for the polymerization of ethylene to polyethylene if it is known that the heat of combustion of ethylene is -1411 kJ/mol and the enthalpy of formation of polyethylene is -248 kJ/mol. Assume that the reaction occurs at constant pressure and temperature of 25°C.

Answer 1

To calculate the enthalpy change for the polymerization of ethylene to polyethylene, we can use Hess's Law, which states that the enthalpy change for a reaction is the same whether it occurs in one step or several steps. In this case, we can consider the polymerization reaction as a two-step process:1. Combustion of ethylene to form CO2 and H2O2. Formation of polyethylene from CO2 and H2OThe overall enthalpy change for the polymerization reaction is the sum of the enthalpy changes for these two steps.Step 1: Combustion of ethyleneC2H4 + 3O2 -> 2CO2 + 2H2OH1 = -1411 kJ/molStep 2: Formation of polyethylene from CO2 and H2On CO2 + 2H2O  ->  C2H4 n + 3nO2H2 = -248 kJ/molSince we are interested in the enthalpy change for the formation of one mole of polyethylene, we need to determine the number of moles of ethylene  n  required to form one mole of polyethylene. The molecular formula of polyethylene is  C2H4 n, so one mole of polyethylene contains n moles of ethylene.Now, we can use Hess's Law to calculate the overall enthalpy change for the polymerization reaction:H_polymerization = H1 + H2H_polymerization =  -1411 kJ/mol  +  -248 kJ/mol H_polymerization = -1659 kJ/molTherefore, the enthalpy change for the polymerization of ethylene to polyethylene is -1659 kJ/mol.