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Combustion of Hydrocarbons

  1. Jul 21, 2016 #1
    1. The problem statement, all variables and given/known data

    I'm currently doing a grade 11 chemistry lab online...So, there's three reactions that we have to interpret...

    1. CH4 + 2 O2 ---> CO2 + 2 H2O
    2. 2 C2H6 + 7 O2 ---> 4 CO2 + 6 H2O
    3. C3H8 + 5 O2 ---> 3 CO2 + 4 H2O

    Now, when I add the theoretical masses of the products for the first reaction (I'll spare the math for now), they add up to mass of the actual masses of the products in the first reaction. However, when I sum the theoretical masses of the products in the second reaction, I don't get the same sum as the actual masses in the second or third reaction. I notice that the actual masses for all three reactions (methane, ethane, and propane) are exactly the same. Is this just because the mass loss in the actual reactions are attributed to waste products and heat, or am I doing something terribly incorrect? Or is there something wrong with my simulation.

    PS - I can provide my math, but I feel as though the program is working fine and that it's just that all hydrocarbon reactions of this sort yield the same product mass no matter what.
     
  2. jcsd
  3. Jul 21, 2016 #2

    epenguin

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    Your stoichiometric equations appear perfectly OK.

    I don't know if the point that is troubling you is just that in order 1, 2, 3 per mole of carbon you have a lower then lower proportion of hydrogen. So in that order, for the same amount of CO2 produced you produce less then less water H2O. The first compound is CH4, you could say the second is equivalent to CH3. Along the series you have fewer C-H bonds and more C-C bonds
     
  4. Jul 21, 2016 #3
    No, the point that is troubling to me is that there's always the same mass of products in each reaction in the online experiment. For example, CH4 + 2 O2 ---> CO2 + 2 H20 yields 292 grams of CO2 and 179 grams of water, and 2 C2H6 + 7 O2 ---> 4 CO2 + 6 H2O yields 292 grams of CO2 and 179 grams of water, and C3H8 + 5 O2 ---> 3 CO2 + 4H2O also yields 292 grams of CO2 and 179 grams of water vapour in the online experiment.
     
  5. Jul 21, 2016 #4

    epenguin

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    Well I can't say more without seeing this online chemistry that is you are trying. If you could post it all verbatim perhaps I could help. Maybe reaction was with a fixed amount of oxygen?
     
  6. Jul 21, 2016 #5
    Yeah, the only thing that changes is the hydrocarbon gas. Methane, Ethane, Propane. But, the masses of CO2 and H2O (as products) don't change.
     
  7. Jul 21, 2016 #6

    epenguin

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    Maybe it's about a fixed amount of oxygen, or maybe there is a product elemental carbon as you had in another problem, but unless I see the original text I'm just guessing what this is about
     
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