The relationship between three state variables, absolute pressure (P), volume (V), and absolute temperature (T), that is deduced from kinetic theory and characterizes an ideal gas is called the ideal gas law, PV = nRT, where P is absolute pressure, V is volume, n is the number of moles of a gas, R is the universal gas constant, and T is temperature. Emil Clapeyron first wrote down the ideal gas law in 1834 although it is a combination of the three empirical gas laws by Robert Boyle, Jacques Charles and Amedeo Avogadro that were known some time before that.

An ideal gas is one in which all collisions between molecules or atoms are perfectly elastic and in which there are no intermolecular attractive or repulsive forces. An ideal gas also obeys Boyle's law, Charles's law, and Avogadro's (or Gay-Lussac's) law. Although no real gas is actually...