(c) Changes in internal energy at constant pressure
Partial derivatives have many useful properties and some that we shall draw on
frequently are reviewed in Mathematical background 2. Skilful use of them can often
turn some unfamiliar quantity into a quantity that can be recognized, interpreted, or
measured.
As an example, suppose we want to find out how the internal energy varies with
temperature when the pressure rather than the volume of the system is kept constant.
If we divide both sides of eqn 2.41 (dU = ƒÎTdV + CV dT) by dT and impose the condition
of constant pressure on the resulting differentials, so that dU/dT on the left
becomes (ÝU/ÝT)p, we obtain