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 

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na