Question

What is the change in enthalpy (ΔH) for the combustion of propane (C3H8) at standard conditions, given that the heat of formation (ΔHf) for propane is -103.85 kJ/mol, and the combustion reaction is:C3H8(g) + 5 O2(g) --> 3 CO2(g) + 4 H2O(l)

Answer 1

To calculate the change in enthalpy  H  for the combustion of propane, we need to use the following equation:H =  Hf products  -  Hf reactants First, we need the heat of formation  Hf  values for all the products and reactants involved in the combustion reaction. The given Hf for propane  C3H8  is -103.85 kJ/mol. We also need the Hf values for O2, CO2, and H2O. The standard Hf values for these compounds are:O2 g : 0 kJ/mol  since it is an element in its standard state CO2 g : -393.5 kJ/molH2O l : -285.8 kJ/molNow, we can plug these values into the equation:H = [3   -393.5 kJ/mol  + 4   -285.8 kJ/mol ] - [1   -103.85 kJ/mol  + 5  0 kJ/mol]H =  -1180.5 kJ + -1143.2 kJ  -  -103.85 kJ H = -2323.7 kJ + 103.85 kJH = -2219.85 kJSo, the change in enthalpy  H  for the combustion of propane at standard conditions is approximately -2219.85 kJ/mol.