WORK CONVENTIONSNATHAN MOOREThere are two different conventions for the work in the first law of thermodynamics: one uses the work doneON the system and the other uses the work done BY the system.Computationally they are equivalentsinceWon=-Wbybut you may be confused and hopefully this short discussion will help you.(1) Work ON the system.ΔE=Q+Won;dE=dQ+dWonErepresents the internal energy of the system,Qthe amount of heat absorbed BY the systemandWonthe work done ON the system by an external agent.Many people prefer to write thefirst law in the above way because it puts the state function,E, on the left side and the two pathdependent functions,QandWonon the right side. Many people like to useWonbecause the aboveequation has a plus sign; the upper division thermodynamics class also uses this convention. Theonly drawback to this convention is that the work is given by the negative of an integralWon=-ZpsysdV(2) Work BY the system.
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