Recall that state functions do not depend on the history of the system (i.e., are independent of path).

Further, recall that fundamental and derived quantities are
**not measurable**.

Because we are always interested in changes ($\Delta$'s) in fundamental/derived quantities, we simply choose reference points, and calculate values as differences from those reference points.

In many problems of interest, we will want to use the "real path" of process since we will be interested in determining the path functions ($Q$ and $W$) as well as possibly $U$ or $H$. Nevertheless, fictitious paths are useful when we are interested in calculating state functions (only), like $U$ and $H$.

Calculate the enthalpy of steam at 200C and 1.5atm relative to a reference state of ice at -10C and 1 atm.