Boltzmann's Analysis of Macroscopic and Microscopic Aspects of Reversible Thermodynamic Processes
Requires a Wolfram Notebook System
Interact on desktop, mobile and cloud with the free Wolfram Player or other Wolfram Language products.
This Demonstration considers three different reversible processes from both a macroscopic and a microscopic point of view: isothermal expansion and compression, isochoric heating and cooling, and adiabatic expansion and compression . Select the process, then use the checkbox to choose between heating–expansion or cooling–compression.[more]
Use the "animate gas particle" button to start the animation. The temperature is indicated schematically on the color bar at the bottom.
At the top left is a pressure-volume plot for each process (isothermal in blue, isochoric in green and adiabatic in orange). Also shown are a piston and cylinder representing these processes. At the right is a schematic representation of the energy level distribution.
Global entropy is defined as the sum of the system entropy variation of the piston and the surrounding entropy variation . In a reversible processes .
When the system entropy change is positive, the entropy change of the surroundings must be negative, and vice versa. Both entropy changes are equal to 0 only in an adiabatic process.[less]
Contributed by: D. Meliga, A. Ratti, L. Lavagnino and S. Z. Lavagnino (August 2022)
Open content licensed under CC BY-NC-SA
Snapshot 1: Isothermal expansion. At constant temperature, expanding the volume causes a compression in the energy-level spacing. As a consequence, more levels are occupied and the system entropy increases ).
Snapshot 2: Isochoric heating. As the energy levels remain unchanged, rising temperature causes increased occupation of higher energy levels. The system entropy thus increases ).
Snapshot 3: Adiabatic expansion. Expansion in volume causes a decreased spacing of the levels. A decrease in temperature leads to decreased occupancy of higher levels. The two effects compensate and the entropy remains constant , ).
 P. Atkins and L. Jones, Chemical Principles: The Quest for Insight, New York: W. H. Freeman, 1999.