Second Law of Thermodynamics

Second Law of Thermodynamics

The second law of thermodynamics is a general principle which places constraints upon the direction of heat transfer and the attainable efficiencies of heat engines. In so doing, it goes beyond the limitations imposed by the first law of thermodynamics. It's implications may be visualized in terms of the waterfall analogy.

Qualitative Statements: Second Law of Thermodynamics

The second law of thermodynamics is a profound principle of nature which affects the way energy can be used. There are several approaches to stating this principle qualitatively. Here are some approaches to giving the basic sense of the principle.

1. Heat will not flow spontaneously from a cold object to a hot object.

2. Any system which is free of external influences becomes more disordered with time. This disorder can be expressed in terms of the quantity called entropy.

3. You cannot create a heat engine which extracts heat and converts it all to useful work.

4. There is a thermal bottleneck which contrains devices which convert stored energy to heat and then use the heat to accomplish work. For a given mechanical efficiency of the devices, a machine which includes the conversion to heat as one of the steps will be inherently less efficient than one which is purely mechanical.