# Combustion homework help

1. Aug 24, 2007

### mojo4king

for eg. combustion of CH4:
CH4(g) + 2O2(g) ---> CO2(g) + 2H2O(l)

enthalpy of combustion: (-393.51) + 2(-241.82) - (-74.81) = -802.34 kj/mol

energy output per unit mass:
802.34 x 1000/16(molar mass) = -50146.25 kj/kg

energy output per unit volume:
-50146.25 x 0.645(mass density) = -32344.33 kj/m3

However I have no clue on how to calculate the carbon dioxide output per unit mass and volume, any help would be kindly appreciated.
Many thanks.

2. Aug 24, 2007

### mbeychok

mojo4king:

I am not sure that I completely understand your questions, but here goes:

(1) The molecular weight of carbon dioxide is 44 and the molecular weight weight of methane is 16. Since the combustion equation shows that 1 mole of methane (when combusted) yields 1 mole of carbon dioxide, that means that 44 mass units of carbon dioxide are formed when 16 mass units of methane are combusted.

(2) Since 1 mole of any gas has the same volume as 1 mole of any other gas, and since 1 mole of carbon dioxide is produced from combusting 1 mole of methane, that means that 1 volume unit of of carbon dioxide is produced for every volume of methane combusted.

Milt Beychok

3. Oct 23, 2007