Pressure-Volume Work for Metastable Liquid and Solid at Zero Pressure.

Unlike with gases, for liquids and solids the pressure of a system can be not only positive, but also negative, or even zero. Upon isobaric heat exchange (heating or cooling) at = 0, the volume work () should be zero, assuming the general validity of traditional equality. This means that at zero pressure, a special process can be realized; a macroscopic change of volume achieved by isobaric heating/cooling without any work done by the system on its surroundings or by the surroundings on the system. A neologism is proposed for these = 0 (and in general, also for non-trivial = 0 and = 0) processes: "aergiatic" (from Greek: , "inactivity"). In this way, two phenomenologically similar processes-adiabatic without any heat exchange, and aergiatic without any work-would have matching, but well-distinguishable terms.