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Homework Help: Pressure Cooker Internal Energy Problem

  1. Feb 15, 2016 #1
    1. The problem statement, all variables and given/known data
    A pressure cooker is a nearly air tight sealed system. When seated on a stove burner and heated, water turns to steam and increases the pressure inside, resulting in higher temperatures so food cooks faster. Suppose 1/2 cup of water is inside the pressure cooker and it is on an active burner on the stove. Suppose that 15000 J of energy vaporize the water and that 4000 J leak out of the system to the atmosphere. What is the name of this kind of process? How much energy is exchanged by heat? Is the energy put in or taken out of the system? How much energy is exchanged by work? Is that work done by or on the system? What is the change in the system's internal energy? (give the sigh of that change as well as the amount)

    2. Relevant equations
    change in internal energy = heat added + work done by system

    3. The attempt at a solution
    For the first question (identifying the type of process) I can't find one that satisfies the situation.

    Isovolumetric has the work done by the system as zero. But the system does work on the gas (increasing its pressure)

    Isothermal has the change of internal energy as zero. But the system takes in 15000 J and leaks out 4000 J so there is an 11000 J difference.

    Adiabatic has the the condition "no heat in or out" but 15000 went in and 4000 went out for a net of 11000 in.

    Isolated has no interaction with surroundings but since 4000 J leak out it is interacting with its surroundings.
  2. jcsd
  3. Feb 15, 2016 #2


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    It is possible for the pressure of a system to increase without any work being done on the system.
  4. Feb 16, 2016 #3
    Thank you that cleared it up for me
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