expansion of a perfect gas into vacuum is related with
Joule expansion The Joule expansion, treated as a thought experiment involving ideal gases, is a useful exercise in classical thermodynamics. It provides a convenient example for calculating changes in thermodynamic quantities, including the resulting increase in entropy of the universe (entropy production) that results from this inherently irreversible process. An actual Joule expansion experiment necessarily involves real gases; the temperature change in such a process provides a measure of intermolecular forces.
Boyle's law This relationship between pressure and volume was first noted by Richard Towneley and Henry Power in the seventeenth century.[5][6] Robert Boyle confirmed their discovery through experiments and published the results.[7] According to Robert Gunther and other authorities, it was Boyle's assistant, Robert Hooke, who built the experimental apparatus. Boyle's law is based on experiments with air, which he considered to be a fluid of particles at rest in between small invisible springs. At that time, air was still seen as one of the four elements, but Boyle disagreed. Boyle's interest was probably to understand air as an essential element of life;[8] for example, he published works on the growth of plants without air.[9] Boyle used a closed J-shaped tube and after pouring mercury from one side he forced the air on the other side to contract under the pressure of mercury. After repeating the experiment several times and using different amounts of mercury he found that under controlled conditions, the pressure of a gas is inversely proportional to the volume occupied by it.[10] The French physicist Edme Mariotte (1620–1684) discovered the same law independent of Boyle in 1679,[11] but Boyle had already published it in 1662.[12] Mariotte did, however, discover that air volume changes with temperature.[13] Thus this law is sometimes referred to as Mariotte's law or the Boyle–Mariotte law. Later, in 1687 in the Philosophiæ Naturalis Principia Mathematica, Newton showed mathematically that if an elastic fluid consisting of particles at rest, between which are repulsive forces inversely proportional to their distance, the density would be directly proportional to the pressure,[14] but this mathematical treatise is not the physical explanation for the observed relationship. Instead of a static theory a kinetic theory is needed, which was provided two centuries later by Maxwell and Boltzmann.