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How to convert J/mol-K to BTU/mol-R?

Discussion in 'Electronics Homework Help' started by Jayce, Jan 25, 2019.

  1. Jayce

    Jayce

    7
    0
    Mar 24, 2018
    Sorry for such question, I don't know where to ask about this but I hope you can help me.

    How to convert J/mol-K to BTU/mol-R? Example 8.314 J/mol-K to BTU/mol-R?

    What I know is that 1 BTU = 1056 Joules and that Kelvin = 1.8 Rankine. So:
    (8.314 J/mol-K)(1 BTU/1056 J)(1 K/ 1.8 R) = 4.3739 x 10^-3 BTU /mol-R. But the answer is supposed to be 1.986.

    Any help would be appreciated, thank you.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    8,830
    1,741
    Nov 17, 2011
    Don't feel sorry for asking, that's what this forum is for.
    I would calculate in the same way as you did, arriving at the same answer.

    Where does the proposed solution come from?
     
  3. Jayce

    Jayce

    7
    0
    Mar 24, 2018
    Thank you for the response. It's from the Universal Gas Constant "R". R = 8.314 J/mol-K = 1.986 BTU/mol-R = 1545 ft-lb/mol-R
    I'm not good at memorization so I plan to just memorized one then learn how to convert it to the other unit/s.
     
  4. Ratch

    Ratch

    1,025
    302
    Mar 10, 2013
    Me thinks you have your units scrambled. I did the calculation for units of calories/(mole-kelvin) and I get 1.986. See below.
    Jayce.JPG
    Ratch
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    8,830
    1,741
    Nov 17, 2011
    Sounds reasonable: cal, not BTU then
     
  6. Jayce

    Jayce

    7
    0
    Mar 24, 2018
    No, the 1.986 should be in BTU/mol-R not cal/mol-K. (Although what you calculated is right if we're talking about cal/mol-K)
    An image below shows the conversion for the universal gas constants. It is from my physics book. (2 different books have the same conversions, so I don't think it's a typo.) Sorry if the image is not good.
     

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  7. Ratch

    Ratch

    1,025
    302
    Mar 10, 2013
    The book's figure of 1545 is for English units of lbf-ft, rankine,and lb-moles. However, the book does not tell you that. Get a different text book.
    Jayce.JPG

    Ratch
     
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