Boyle's law of the gas, and "k" is a constant. The equation states that the product of pressure and volume is a constant for a given mass of confined gas and this holds as long as the temperature is constant. For comparing the same substance under two different sets of conditions, the law can be usefully expressed as The equation shows that, as volume increases, the pressure of the gas decreases in proportion. Similarly, as volume decreases, the pressure of the gas increases. The law was named after chemist and physicist Robert Boyle, who published the original law in 1662. This relationship
Molar volume an ideal gas: Hence, for a given temperature and pressure, the molar volume is the same for all ideal gases and is known to the same precision as the gas constant: "R" = 0.082 057 338(47) L atm K mol, that is a relative standard uncertainty of 5.7×10, according to the 2014 CODATA recommended value. The molar volume of an ideal gas at 100 kPa (1 bar) is The molar volume of an ideal gas at 1 atmosphere of pressure is For crystalline solids, the molar volume can be measured by X-ray crystallography. The unit cell volume ("V") may be