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Homework Help: Find the final volume

  1. Dec 21, 2008 #1


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    1. The problem statement, all variables and given/known data
    Two ideal gas (n mole A and m mole B) was separated by a piston (impermeable and diathermal) the whole setup is confine in a adiabatic walls so no heat exchange with outside. Let the piston move, at equilibrium, find the final volume. Assume the final temperature of both gas is T and the total volume is V.

    2. The attempt at a solution
    First of all, both gas satisfy ideal gas state equation

    \frac{P_AV_A}{T_A} = nR, \qquad \qquad \frac{P_BV_B}{T_B} = mR

    Since we know the final temperature, and at equilibrium, the pressure is the same on both compartment (otherwise, the piston will move), so assuming the final volume of A is [tex]V_A[/tex], then the final volume of B will be [tex]V-V_B[/tex], we conclude that

    \frac{P}{T} = nRV_A = \frac{P}{T} = mR(V-V_A)

    We can solve for [tex]V_A[/tex] and [tex]V_B[/tex], right?
  2. jcsd
  3. Dec 22, 2008 #2


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    Your setup looks correct, except for a mathematical error...
    If [itex]\frac{P V}{T} = n R[/itex], then [itex]\frac{P}{T} = \cdots [/itex] ?

    By the way, once you have found the answer, it'll be nice trying to explain its physical meaning and saying something about whether you could have foreseen the outcome.
  4. Dec 22, 2008 #3


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    Oh, careless. Thanks
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