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Reversible Heating and Cooling

  1. Oct 6, 2009 #1
    1. The problem statement, all variables and given/known data

    I have two problems.

    What is Delta U, Delta H, q, and w for the Reversible heating of an ideal gas at constant P.

    Also, what are these values for the Reversible cooling of an ideal gas at constant V.

    2. Relevant equations

    3. The attempt at a solution

    For the first equation I decided that all values would be negative except for heat which is positive. I consider this because w=-pex(deltaV) and I decided q= positive because when u are heating somethign you add heat.

    for the second problem I know work=0 because the system is at constant volume. Also, q=Delta U because Delta U=q+w. q is negative because soemthing that is cooling is removing heat. I can not figure out delta H.
  2. jcsd
  3. Oct 6, 2009 #2


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    Welcome back to PF :smile:

    Are you being asked to provide the expressions for ΔU, etc., in terms of P and V? Or just to state whether they are positive, negative, or zero?

    That's good reasoning on w and q. How did you figure out that U and H are negative?

    Looks good so far.
    What is the definition of H?

    Also, the fact that it is an ideal gas might or might not come into play.
  4. Oct 6, 2009 #3
    H is enthalpy. I just have to say whether or not the values of these will increase decrease or if they are zero in each case. I am really only concerned about the last two.
  5. Oct 7, 2009 #4


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    How is enthalpy H defined in terms of U, P, and V? You can use this defining equation to work out whether ΔH is +, -, or 0.
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