Second Law of Thermodynamics

The First Law of Thermodynamics is an extremely powerful bookkeeping tool — it insists that energy is always conserved in every process — but, as the next subsection shows, it leaves two important, very practical questions completely unanswered. Closing those gaps requires an entirely separate, additional principle: the Second Law of Thermodynamics, developed across the two subsections that follow — first the specific limitations of the First Law that motivate t …