If a pork roast must absorb 1700kj to fully cook, and if only 11% of the heat produced by the barbeque is actually absorbed by the roast, what mass of co 2 is emitted into the atmosphere during the grilling of the pork roast?

Let us  assume propane was the fuel
C3H8(g) + 5O2(g) ---> 3CO2(g) + 4H2O(g) = 2217kJ
1 mole ofpropane produces 3 moles of CO2 
heat absorbed by pork = 0.11 x 2217
                                     = 243.87 kJ/mol
number of moles of propane = 1700kJ / 243.87 kJ/mol
                                              = 6.971 moles
1 mole of C3H8 = 3 moles ofCO2
6.971 moles of C3H8 = ?
3 x 6.971 = 20.913 moles of CO2
Convert to grams
mass = MW x mole
          = 44 x 20.913
          = 920.172g of CO2 emitted