 In 1854, Clausius introduced the notion of the “equivalence value” of a transformation, a concept that is the ancestor of the modern day concept of entropy. Later in 1865 Clausius coined the term “entropy” for a similar concept (the word derives from the Greek word for transformation). The entropy of a state \(A\), \(S(A)\) is defined as the integral \(S(A) = \int^{A}_{O} dQ/T\) over a reversible transformation, where \(O\) is some arbitrary fixed state. For \(A\) to have an entropy, the transformation from \(O\) to \(A\) must be quasi-static, i.e., a succession of equilibrium states. Continuity considerations then imply that the initial and final states \(O\) and \(A\) must also be equilibrium states. Put in the language of entropy, the Second Law states that in a transformation from equilibrium state \(A\) to equilibrium state \(B\), the inequality \(S(B) - S(A)\) is greater than or equal to the \(\int^{A}_{B} dQ/T\). Loosely put, for realistic systems, this implies that in the spontaneous evolution of a thermally closed system the entropy can never decrease and that it attains its maximum value at equilibrium. We are invited to think of the Second Law as driving the system to its new, higher entropy equilibrium state.