Macroscopic Approach
a) The irreversibility of real processes and the inadequacy of First Principle to describing it: focus on emblematic
types of spontaneous and irreversible transformations (free expansion of a gas, heat transfer from a body at a higher
temperature to a body at lower temperature, dissipation of mechanical - electric - energy by friction).
b) The spontaneous evolution of natural processes as a “fact of nature” elevated to a principle: the Second
Principle of thermodynamics and its different statements as special cases of a general principle “If a system
spontaneously evolves from an equilibrium state to another, such transformation is irreversible: there is no
transformation that can produce the only result of bringing the system back to its initial conditions”.