The numerical value of R depends upon the units in which pressure and volume are expressed. When pressure is expressed in atmosphere and volume in litres, then the value of R at STP for 1 mole of gas is $\, \, \, \, \, \, \, \, \, \, R=\frac{1 atm \times 22.414\, L}{1 mole \times 273.15\, K}$ $\, \, \, \, \, \, \, \, \, \, = 0.082 L atm K^{-1} mol^{-1}$
The gas laws were developed at the end of the 18th century, when scientists began to realize that relationships between pressure, volume and temperature of a sample of gas could be obtained which would hold to approximation for all gases.
The five gas laws are:
Boyle’s Law, which provides a relationship between the pressure and the volume of a gas.
Charles’s Law, which provides a relationship between the volume occupied by a gas and the absolute temperature.
Gay-Lussac’s Law, which provides a relationship between the pressure exerted by a gas on the walls of its container and the absolute temperature associated with the gas.
Avogadro’s Law, which provides a relationship between the volume occupied by a gas and the amount of gaseous substance.
The Combined Gas Law (or the Ideal Gas Law), which can be obtained by combining the four laws listed above.