The classical adiabatic constancy of PVγ for an ideal gas,can be shown to be a quantum mechanical occurrence,which yields the particular value of the constant,in question

In this paper we find a full connection between the long lasting macroscopic classical laws of gases and the quantum mechanical description of non-interacting particles confined in a box,thus constituting an ideal gas. in such a gas,the motion of each individual molecule can be considered to be independent of all other molecules,and the macroscopic parameters of an ideal gas,mainly,pressure p and temperature t,can be defined as simple average quantities based on individual motions of all molecules in consideration. it is shown that for an ideal gas enclosed in a macroscopic cubic box of volume v,an alphanumeric expression for the constant appearing in the classical law of adiabatic expansion law,i.e. pv5/3 = constant,can be derived based on quantum mechanics. note that this constant has otherwise remained for centuries,as just an abstract quantity in the form of p1v 1 5/3=p2v2 5/3 = p 3v3 5/3 written for different thermodynamic states,delineated through an adiabatic transformation. no one even seems to have thought that it may eventually have a particular expression. physical implications of the result we disclose are discussed. © 2012 tibtd printed in turkey.