Limitations of First Law of Thermodynamics
The first law of thermodynamics is a law of conservation of energy. It does not specify the direction of the process. All spontaneous processes processed in one direction only. The first law of thermodynamics does not deny the feasibility of a process reversing itself. The first law of thermodynamics does not provide answers to the following questions.
IS A PARTICULAR PROCESS / REACTION FEASIBLE?
TO WHAT EXTENT DOES THE PROCESS / REACTION PROCEED?
IS COMPLETE CONVERSION OF INTERNAL ENERGY INTO WORK POSSIBLE? |
There exists a law which determines the direction in which a spontaneous process proceeds. The law, known as the second law of thermodynamics, is a principle of wide generality and provides answer to the above questions.
It is essential to understand the meaning of the following terms in order to discuss the second law of thermodynamics:
- Thermal reservoir is a large body from which a finite quantity of energy can be extracted or to which a finite quantity of energy can be added as heat without changing its temperature.
- A source is a thermal reservoir at high temperature from which a heat engine receives the energy as heat.
- A sink is a low temperature thermal reservoir to which a heat engine rejects energy as heat.
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