Why displacement used in thermodynamics?

Answer 1

Many of the properties measured and calculated in thermodynamics are "state" functions. The key feature is not their absolute value but rather how much they change. We are more concerned with the amount of work required to raise an object 20 feet than we are with the total potential energy of the object. We are more concerned with the change in enthalpy involved with condensing a ton of steam than some absolute enthalpy of the steam. For this reason most thermodynamic properties are tabulated relative to a "reference state". As long as the same reference state is used for both the initial and final conditions, we will always get the same difference between the two, no matter what reference state is chosen. In this respect, we are more interested in how far we are displaced from the reference state as changes are made in a system.

Answer 2

Displacement in thermodynamics is used as a measure of the change in volume of a system. It helps describe how the system's volume changes during a process, such as in a piston-cylinder arrangement. By considering displacement, we can analyze how the system's internal energy, work, and heat exchange are affected by changes in volume.