Question

Calculate the enthalpy change of the polymerization reaction of ethylene, given that the heat of combustion of ethylene is -1411 kJ/mol and the enthalpy of formation of ethylene is +52.3 kJ/mol. The balanced equation for the polymerization of ethylene is:nC2H4 -> [-C2H4-]nAssume complete polymerization and that the standard enthalpy of formation of the polymer is negligible.

Answer 1

To calculate the enthalpy change of the polymerization reaction of ethylene, we can use Hess's Law. According to Hess's Law, the enthalpy change of a reaction is the same whether it occurs in one step or several steps. In this case, we can consider the polymerization reaction to occur in two steps:1. Formation of ethylene from its elements  Hf 2. Combustion of ethylene to form the polymer  Hc The overall enthalpy change of the polymerization reaction  Hr  can be calculated as follows:Hr = Hf - HcGiven that the enthalpy of formation of ethylene  Hf  is +52.3 kJ/mol and the heat of combustion of ethylene  Hc  is -1411 kJ/mol, we can calculate the enthalpy change of the polymerization reaction  Hr :Hr = 52.3 kJ/mol -  -1411 kJ/mol Hr = 52.3 kJ/mol + 1411 kJ/molHr = 1463.3 kJ/molTherefore, the enthalpy change of the polymerization reaction of ethylene is +1463.3 kJ/mol.