One of the main empirical ideal-gas laws was established in 1662 by R. Boyle, and independently in 1676 by E. Mariotte. According to Boyle’s Law, at constant temperature (and low pressure) the volume V of a gas mass M is inversally proportional to its pressure p, i.e., pV = const. This law represents a description of the isothermal process of ideal gas.

The joint analysis of Boyle’s law and the empirical *Charles’*, Gay–Lussac’s and *Avogadro’s laws* can lead to the universal Equation of State of ideal gas — *the Clapeyron (Clapeyron–Mendeleyev)* equation.
where
is the molecular mass of gas, R is the universal gas constant (R = 8.314 J/mole K), and T is the absolute temperature.

This equation was subsequently rigorously substantiated by the molecular kinetic theory according to which p = nkT, where n is the number of molecules in unit volume, k is the *Boltzmann constant* (k = R/N_{A}, N_{A} = 6.022 10^{23} mole^{−1} is the Avogadro number, k = 1.381 10^{−23} J/K), from which follows the ideal gas equation of state and, accordingly, the expression for Boyle’s law.

As with the other ideal-gas laws, Boyle’s law is applicable at pressures far from critical, i.e., in that region of state, where one may neglect: a) the proper size of particles as compared to the interparticle distance; and b) the forces of interparticle interaction, where the energy of this interaction is considerably lower than the kinetic energy of particles.

Heat & Mass Transfer, and Fluids Engineering