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Revision as of 11:07, 8 June 2009 by Dduque (talk | contribs) (W=-pdV on compression or expansion, but always ''upon'' (I am 98% sure))
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The mechanical work, W, performed upon a gas is given by

W = - \int_\alpha^\beta p ~dV

where \alpha and \beta are points in state space, p is the pressure and V is the volume. The mechanical work done by the gas has the opposite sign (a common source of mistakes).

For reversible changes,


and for irreversible changes

\left.dW\right. > -p~dV