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Homework Help: AvLaw - Which is the correct method of finding moles of gases?

  1. Dec 17, 2017 #1
    1. The problem statement, all variables and given/known data
    Based on your understanding of Avogadro's law.
    1000 L steel storage tank contains 88.5 kg of methane gas, CH4.
    Calculate no. of moles.

    3. The attempt at a solution
    one method= no. of moles=mass/molar mass.
    no. of moles= 88500/16.04= 5517.4 moles.

    other method= 1 mol= 22.4 liter.
    no of moles= 1000 L/22.4L= 44.6 moles.

    Please inform me of the correct method, thanks!
  2. jcsd
  3. Dec 17, 2017 #2

    Charles Link

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    The 22.4 L for one mole is only at S.T.P.=Standard temperature and pressure. They did not specify the temperature, but the much bigger factor here is the gas in the container is undoubtedly pressured. Assuming it is at standard temperature (zero degrees Centigrade), you could compute the pressure in atmospheres by taking the ratio of your first answer divided by your second (incorrect answer).
  4. Dec 17, 2017 #3
    So 5517.4 moles is the correct number of moles? since they didn't specify the temp.
  5. Dec 17, 2017 #4

    Charles Link

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    Yes, it is correct, regardless of the temperature. Upon being given the temperature, it would also be possible to compute the pressure. You would find that the gas is highly pressurized, unless it is being kept at very low temperature.
  6. Dec 17, 2017 #5
    Oh by using the ideal gas law, ok thanks!
  7. Dec 18, 2017 #6


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    Your first answer was correct. How could you doubt it?
    In this and other questions you have shown yourself to have some grasp but were easily distracted and confused by irrelevancies. Things that were related to a question but made you miss a point.
    So having been partially successful and activated it is a good time, I recommend, to go back and do some revision in order to get the concepts fixed securely in your mind. :smile:
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