Other statements of Second Law of Thermodynamics

Physics

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Second Law in terms of efficiency

The second Law of thermodynamics gives a fundamental limitation to the efficiency of a heat engine and the co-efficient of performance of a refrigerator. In simple terms, it says that the efficiency of a heat engine can never be unity.

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Kelvin Planck statement

No process is possible whose sole result is the absorption of heat into a reservoir and its complete conversion into work.

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Clausius statement

No process is possible whose sole result is the transfer of heat from a colder body to a hotter body.

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Qualitative statement of Second Law of thermodynamics

Qualitative statement of Second Law of Thermodynamics:
It is not possible to design a heat engine which works in cyclic process and whose only result is to take heat from a body at a single temperature and convert it completely into mechanical work.

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Physical examples of Second Law of Thermodynamics

Physical examples of Second law of thermodynamics are as follows:
1. An internal combustion engine in a car converts chemical energy from the gasoline to heat to forward motion. The best efficiency we could get is something on the order of 35%, and that's the absolute best we can do, ignoring friction losses and the like. (The exact maximum efficiency is dependent on the temperature of the combustion and the heat sink, i.e. ambient).
2. Heat flows from bodies with higher temperature to the lower temperature and not vice versa.
3. Work can be converted completely into heat as in case of a resistor but heat cannot be completely converted into work as is in the case of a heat engine.
4. A drop of dye when placed in a beaker of water will eventually result in an evenly coloured solution, even without stirring. The dye molecules diffuse and spread itself as evenly as possible throughout the volume of water.

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Identify whether a process follows or violates Second Law of Thermodynamics

The process which follow second law of thermodynamics:
1. A drop of dye when placed in a beaker of water will eventually result in an evenly coloured solution, even without stirring. The dye molecules diffuse and spread itself as evenly as possible throughout the volume of water. 
2. Making snowballs will always make ones hands colder, because thermal energy always flows in a hot-to-cold direction. No material can spontaneously gain thermal energy from colder surroundings. This is because it would require the energy to become spontaneously more concentrated in order for the opposite process to occur. That is, this would involve a spontaneous increase in organization of molecules or energy which would mean the opposite of energy spreading out.
A device that violates the Second Law of Thermodynamics is formally known as a perpetual motion machine of the second kind. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an energy source. This kind of machine is impossible, as it would violate the first or second law of thermodynamics.

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