Question

how do i calculate the mass of CO2 emitted per Kj of heat produced in a combustion reaction?

Answer 1

The heat produced by a combustion reaction will vary depending on which hydrocarbon is burned, so let's use the simplest one as an example:\[CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O\]
the heat of combustion for this reaction is -891 kJ/mol, so every mole of CH4 that burns produces 891kJ of heat energy. Because the reaction ALSO produces 1 mole of CO2, the burning of 1 mole of methane produces 1 mole of CO2 as well.
1 mole of CO2 weighs 44g, so if you need the energy PER GRAM, then divide the energy per mole by the molar mass of CO2 (44g/mol)