A. Schadicchio, ICTP

This lesson starts by clarifying some aspects related with the second law of thermodynamics like the Clausius theorem. An example of the validity of this theorem is a cycle where one of the processes is irreversible, a gas suddenly expand from volume V_{A } to volume V_{B} and then the gas is compressed again to volume V_{A } using a reversible isothermal transformation. For finishing the entropy topic the Sakur-Tetrode equation is introduced, this equation incorporates quantum considerations in the expression for the entropy of a monatomic classical ideal gas. Then the Sackur–Tetrode equation is conveniently expressed in terms of the thermal de Broglie wavelength and the importance of quantum physics to accurately calculate macroscopic quantities, like the pressure, was shown by calculating the equilibrium pressure of a liquid with its vapor at temperature T when a mole of substance is evaporated.