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Work Conventions

# Work Conventions - WORK CONVENTIONS NATHAN MOORE There are...

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WORK CONVENTIONS NATHAN MOORE There are two different conventions for the work in the first law of thermodynamics: one uses the work done ON the system and the other uses the work done BY the system. Computationally they are equivalent since W on = - W by but you may be confused and hopefully this short discussion will help you. (1) Work ON the system. Δ E = Q + W on ; dE = dQ + dW on E represents the internal energy of the system, Q the amount of heat absorbed BY the system and W on the work done ON the system by an external agent. Many people prefer to write the first law in the above way because it puts the state function, E , on the left side and the two path dependent functions, Q and W on on the right side. Many people like to use W on because the above equation has a plus sign; the upper division thermodynamics class also uses this convention. The only drawback to this convention is that the work is given by the negative of an integral W on = - Z p sys dV (2) Work BY the system.
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