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Hydrocarbon reaction

  1. Sep 27, 2015 #1
    Dear PF Forum,
    First of all, I'd like to thanks PF Forum for giving me invaluable answers all this time.
    Now, I have a "situation" here.
    My church wants to conserve environment by changing cooking oil into biodiesel from its parishioners
    I'd like to know how effective this effort is.
    I have many, many questions regarding biodiesel, car gasoline, hydrocarbon, etc...
    But in this post, I'd like to know these simple facts first.
    1. How much energy is released by reactiing 2 moles CH4 + 5 moles O2 -> 2 moles CO2 + 8 moles H2O. How many joules (or calories equivalent) are released in this process?
    2. How many joules/calories are released by this reaction? 2C8H18 + 25O2 -> 16CO2 + 18H2O. All are in moles unit and given the ideal condition where carbon monoxyde are not produced.
    3. Is it true that CH4 is considered "cleaner" than C8H18?
    4. If that so, why?
    Is it because for ...
    4A. 1824 gr CH4 produces 5016 gr CO2 and 1824 gr C8H18 produces 5632 gr CO2?
    4B. Given that I don't know the answers of question 1 and 2.
    That for 1824 gr CH4 produces more (is it true more?) energies than 1824gr C8H18?
    4C. Still that I don't know the answers of question 1 and 2:
    That for every kg CO2 produced, CH4 releases more (is it true, more?) energies than C8H18?
    These questions might not have anything to do with biodiesel. But I'd like to study some basic chemistry first.
    Thanks for any help.
     
  2. jcsd
  3. Sep 27, 2015 #2

    Bystander

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  4. Sep 27, 2015 #3
    Wow, that was fast! Thanks Bystander.
    It's not I haven't googled. I have visited many links, but none gave specific answer like the link you give me.
    Let me see if I understand this reaction correctly.
    As stated in Wiki, the heat combustion of 1 Kg octane is 44 MJ. So 1 mole C8H18 + n O2 -> .... will produce 114 gr * 44 MJ = 5.015 MJ?
     
  5. Sep 27, 2015 #4

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    ..., given that your calculator is working properly.
     
  6. Sep 27, 2015 #5
    And it's about 5.06478 MJ per moles. I forgot to include 44.427 MJ/Kg. I type 44 MJ/Kg. Okay, thanks I'm convinced that I'm on the right track.
    So about CH4 issue.
    The heat combustion for
    1 kg CH4 is 50.009 MJ
    1 kg C8H18 is 44.27 MJ.
    Consequently
    1 kg methane will produce 2.75 kg CO2
    1 kg octane will produce 3.09 kg CO2

    Why is methane considered cleaner than gasoline which has higher octane ratio in it?
    Is it because
    A. 1 kg CH4 produces higher energy than 1 kg octane?
    B. 1 kg methane produces lower CO2 than 1 kg octane?
    C. Methane produces 18.185 MJ per 1 kg CO2 released, while Octane produces 14.388 MJ per 1 kg CO2 released? After doing the calculation.
    I think the answer is C if we focus on lower pollution.
    Is my opinion correct?
     
  7. Sep 27, 2015 #6

    Bystander

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    That's the basis for the assertion.
     
  8. Sep 27, 2015 #7
    Thanks. Now, I can focus on biodiesel after some online researches.
     
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