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First Law of Thermodynamics and ideal gas

  1. May 19, 2008 #1
    1. The problem statement, all variables and given/known data
    An ideal gas expands isothermally, performing 3.40x10^3 J of work in the process.
    a) The change in internal energy of the gas
    b) The heat absorbed during this expansion


    2. Relevant equations
    [tex]\Delta[/tex]U=Q-W


    3. The attempt at a solution
    a) Since it's isothermally expanding, there will be no change in internal temperature, so:
    [tex]\Delta[/tex]U=0

    b) Q=W, so:
    Q=-3400 J
     
  2. jcsd
  3. May 19, 2008 #2

    Mapes

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    Science Advisor
    Homework Helper
    Gold Member

    Looks good, as long as positive heat means that the system is heating the environment and positive work means that the environment is doing work on the system. This sign convention is a little unconventional, though.
     
  4. May 19, 2008 #3

    Doc Al

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    Staff: Mentor

    Good.
    How did that negative sign sneak in? (W is positive, so Q is positive.)
     
  5. May 19, 2008 #4
    Ah, ok. That was a silly mistake, lol :)

    So Q=3400 J
     
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