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What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What mass

  1. Nov 2, 2012 #1
    1. What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What mass of CO2 is produced?

    C4H10 + 13/2 O2 --> 4 CO2 + 5 H2O
    Heat of reaction = -2658 kJ



    2.



    3. Mass of butane = 33g

    Mass of CO2 = 176.04g <-- This is wrong and the right answer is 99g CO2





    How is that so.. :eek:
     
  2. jcsd
  3. Nov 2, 2012 #2
    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    I think the reaction is exothermic. What it gives you is the overall delta H. In order to find what amount of butane is necessary to produce 1.5x10^3 kJ of energy(exothermic since its being released) is just a stochiometry problem. Here is a start.

    -1.5x10^3 kJ(58.12g/-2658 kJ)=33 grams of Butane.

    Now figure out how much CO2 is released.
     
  4. Nov 2, 2012 #3
    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    Thanks for answering... but why would you even need to know that to figure out how much CO2 was produced? Isn't it right there
     
  5. Nov 3, 2012 #4

    Borek

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    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    176 g of CO2 is produced from 1 mole of butane. 33 g of butane is not 1 mole.
     
  6. Nov 3, 2012 #5
    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    Oh right! How would I solve it then?
     
  7. Nov 3, 2012 #6
    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    33 / 58.12 = 0.567
    176 x 0.567 = 99.7
     
  8. Nov 3, 2012 #7

    Borek

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    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    Best approach is to try first, ask questions later.

    Wasn't that hard.
     
  9. Nov 3, 2012 #8
    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    Not really but if people were more inclined to solve the problem as an example, it would make learning go a lot quicker.
     
  10. Nov 3, 2012 #9

    Borek

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    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    Actually - not. The more problems you try to solve by yourself, the better your general solving skills will be. Otherwise you will learn how to deal with hundreds of known problems, but you will be still helplessly lost whenever facing a new one.

    Unfortunately that's the way schools work these days - they teach how to reproduce the solution, not how to solve the problem.

    If some of us know to solve the problem at first sight it is not because we did similar problem in teh past, but because we know how to approach every problem. Believe it or not, but filling our template is a first step.
     
  11. Nov 3, 2012 #10
    Re: What mass of butane in grams is necessary to produce 1.5 x 10^3 kJ of heat? What

    You are so knowledged. Tell me more tips to get good at chemistry.
     
  12. Feb 10, 2014 #11
    How did you get 176g of CO?

    I don't understand where the 176g of CO2 came from...
     
  13. Feb 10, 2014 #12

    Borek

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    Neither do I :wink:

    176g of CO2 is produced when you burn 1 mole of butane. Question doesn't ask about 1 mole of butane, so 176g is not a correct answer. It is a correct answer to some other question.

    Actually for every number you can construct a problem that the number will be a correct answer.
     
  14. Feb 10, 2014 #13
    I'm lost on how to solve this problem still...I got the 33g of butane but am not sure how to get to the 99g of CO2.

    And I agree with you about working problems out on our own first in order to learn but I have been looking at this one for way too long!
     
  15. Feb 10, 2014 #14

    Borek

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    Staff: Mentor

  16. Feb 10, 2014 #15
    Phew, thank you! I appreciate your help. It all makes sense now :)
     
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