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. [7 marks) b) In a different combustion process isooctane, CH 18, 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. [2 marks] ii) Calculate the enthalpy for the stoichiometric combustion of isooctane at 25 C and 1 atm using the following enthalpy of formation data: Isooctane Carbon dioxide Water hi (kJ kmol-1) -259300 -393546 -285834 [3 marks] iii) The value calculated in part (ii) corresponds to the higher heating value for isooctane. How and why would the lower heating value differ? [3 marks]