Summary: Forms of Work in the First Law

From the the first law of thermodynamics

$$dU = dq + dw$$ (08-1)

We identified the work associated with various types of physical processes. For the case of a magnetic and polarizable solid we have:

$$\input{equations/extra-work}$$ (08-2)

The extra terms could include chemical work, work to add or subtract charge from a body, potential energy in a gravitational field, etc.

For the special case of a non-polar, non-magnetic fluid, that cannot change its composition, the work is simply:

$$\input{equations/pdvwork}$$ (08-3)

Systems that have Equation 8-3 as the only type of work term will be called simple pure fluids.

Questions: Why does the $V$ term appear in front of the terms in Eq. 8-2 and not in front of Eq. 8-3? Why is there a ``minus sign difference''? Could Eq. 8-3 be modified so it also have a ``reference volume term'' out front?