The Second Law of Thermodynamics

Abstract

The first law of thermodynamics expresses the existence of the energy function U as a consequence of the conservation of energy; therefore, the change in energy, ΔU, for any process must take place without violating the conservation of energy whether a process is possible or impossible. For example, the first law does not rule out the spontaneous heat transfer from a lower temperature to a higher temperature so that a pencil at a uniform temperature may become hotter at one end and colder at the other without external interference. Such processes do not violate the first law so long as the conservation of energy prevails, i.e., the decrease in energy of one end of the pencil is compensated by the increase in energy of the other end. It is the second law of thermodynamics that sets the criterion for the impossibility of such processes.