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Homework Help: Work (Thermodynamics)

  1. Jan 17, 2005 #1
    I am confused about work. If I do positive work ON a gas, does the volume decrease on increase? Essentially, I am just confused about when work is negative and when it is positive. Hopefully someone can clarify this for me.

  2. jcsd
  3. Jan 17, 2005 #2


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    Differential work is defined as
    [tex] \delta W=:-pdV [/tex]

    in the case of a gas which doesn't interact with the surroundings through other means.


    PS.Judge it for yourself...
  4. Jan 17, 2005 #3


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    It takes work to compress a gas, but it takes no work at all to let one expand.

    - Warren
  5. Jan 17, 2005 #4


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    dE = δq + δw , differential change in internal energy of a system equals the sum of the heat added to the system plus the work done on the system, where δw = - PdV, and dE = δq - δw, diff. change in energy equals heat added minus the work done by the system, where w = PdV. The first statement is commonly (not always) used in chemical thermodynamics, and the second is commonly used by engineers and physicists. dV is positive for an increase in the volume of the system for both statements; the distinction in the sign of w is made when one considers whether work is defined to be done on or by the system. Chemists emphasize the system, engineers and physicists emphasize the work.
  6. Jan 19, 2005 #5
    Belly Button

    our teacher keeps telling us this to remember work - you know how people can either have innie or outie belly buttons? well, most people have innies, but there are outies, too. since most people have innies, innies are thought of as "good". Now, if work is going into the gas (innie) then work is positive. if work is going out of the gas (outtie) it's negative. weird, but it works! (hahah no pun intended) :wink:
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