Path Functions

The properties which depend on the path are called path functions. For example, work $(W)$ and heat $(Q)$.

A path here refers to the sequence of situations the system passes through while a change of state is being brought about (section 4.2.4). Unlike state functions, work and heat are not properties a system possesses in a given state — they appear only while a change is occurring, as energy in transit between the system and its surroundings. Two different paths connecting the same initial and final states generally involve different amounts of work and heat, even though every state function changes by exactly the same amount either way. This is why $W$ and $Q$ carry information about *ho …