a) Propane, C3H8, is completely combusted in 150 % stoichiometric air. Determine the air-fuel ratio for this process assuming that air contains only oxygen and nitrogen in a molar ratio of 1:3.76 and its molecular weight is 29.

b) In a different combustion process isooctane, C8H18, is completely burnt with a stoichiometric amount of air at 298 K. The products exit the combustion chamber at this temperature.

i) Assuming that air contains only oxygen and nitrogen in a molar ratio of 1:3.76 write the balanced chemical equation for the complete combustion of isooctane with theoretical air.

ii) Calculate the enthalpy for the stoichiometric combustion of isooctane at 25 C and 1 atm using the following enthalpy of formation data: (kJ kmol-1) Isooctane -259300 Carbon dioxide -393546 Water -285834 iii) The value calculated in part (ii) corresponds to the higher heating value for isooctane. How and why would the lower heating value differ?