Q + W = u

_{2}- u

_{1}

Q = u

_{2}- u

_{1}+ p(v

_{2}- v

_{1})

Since h = u + pv, Then

Q = h

_{2}- h

_{1}

The first equation states that the sum of heat and work done is equal to the change in internal energy, I can comprehend up to there. But in the next line the work done is taken to the other side of the equation; both mathematically and physically I cannot understand how the work done (p(v

_{2}- v

_{1})) is still positive.

Mathematically I would say that taking work to the opposite side would make work negative.

Physically I would think that the amount of heat supplied/given off would be equal to the difference of initial and final internal energy minus the work done.

Hope someone could clear this out for me. Thanks