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Homework Help: Work done by a gas during an adiabatic process involving a state chang

  1. Apr 28, 2014 #1
    1. The problem statement, all variables and given/known data
    The problem involves a container holding a gas at high pressure. The container is opened to the environment, where the gas will cool down, producing a liquid or solid, and I want to find the work done by the gas throughout this process.

    2. Relevant equations
    PV^γ = constant
    U = Cv (ΔT)

    3. The attempt at a solution
    The process that I would do is find the new values of the P, V after the expansion using PV^γ = constant, find out the new temperature, and use the change in internal energy associated with the temperature to find the work, as in an adiabatic process the heat flow is 0. However, with the phase change, I'm not really sure on how to best do this.

    Currently, I'm thinking that the best way to do this would be to do the adiabatic expansion until the sublimation or boiling point, calculate the work as above, then calculate the work by determining the change in volume from the gaseous to the liquid or solid phase, then using -PΔV to determine the work due to phase change, with P being the atmospheric pressure.

    Can anyone tell me if I'm in the right direction, or if there is something I'm missing?
  2. jcsd
  3. Apr 29, 2014 #2
    I don't think this is an adiabatic process.

    First of all, if the gas is at high pressure and then opened to the environment wouldn't it immediately expand and mix with the atmosphere through convection?

    Secondly, in a phase change their is an exchange of heat. The value of this amount of heat depends on the latent heat of condensation of the gas.
  4. Apr 29, 2014 #3

    Andrew Mason

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    Science Advisor
    Homework Helper

    Perhaps you could give us the exact wording of the question.

    Is this an ideal gas? If not, why would PV^γ = constant and U = Cv (ΔT) apply? If so, why would it turn to solid or liquid?

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