Question

Calculate the enthalpy of combustion of ethylene at 300 K at constant pressure if it's enthalpy of combustion at constant volume is -1406 kJ/mol

Answer 1

enthalpy of combustion at constant pressure =enthalpy of combustion at constant volume +delta nRT

delta n=number of moles ofgasious products -number ofmoles of gaseous reactanst
so for C2H4(g)+3O2(g)==>2CO2(g)+2H2O(l) is
2-(3+1) =-2
enthalpy at constant pressure =-1406Kjmol^-1 +[-2 mol *8.314*10^-3kJmol^-1K^-1*300K]
=-1406KJmol^-1 +(-4.9884KJmol^-1)
= -1411KJ/mol is the answer