Second law of Thermodynamics|Thermodynamics ka dusra niyam

 

Second law of Thermodynamics.

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Today we are concern about 2nd law of Thermodynamics. I think it will be helpful for you for level of sr. Sec. And gratuation level .

Second law of Thermodynamics 

The first law of thermodynamics establishes an exact relation between heat and work. It follows directly from this law that it is impossible to get work from any machine without giving it an equivalent amount of energy in any form. In other words, this law is merely the generalisation of the law of conservation of energy including heat energy and states that the energy of the universe remains constant.

The first law of thermodynamics tells us that heat and mechanical work both are interconvertible. This does not tell us the limitation and condition for this conversion i.e., how much heat is converted into work and whether the transformation itself can take place or not (the direction of energy transformation). The law specifying the condition of transformation of heat into work is called the second law of thermodynamics.

Kelvin's statement of the second law:

It states that:It is impossible to get continuous supply of work by cooling a body with  temperature lower than that of the coldest of its surroundings."

                                    or

"A transformation whose only final result is to transform into work the heat extracted from a source which is at the same temperature throughout is impossible."

Clausius statement of the second law 

It is impossible for a self acting machine, unaided by any external agency to transfer heat from one body to another at a higher temperature".

It is impossible for any cyclic machine to produce no other effect than to convey hent continuously from one body to another at a higher  temperature".

Both the statements of the second law are equivalent. Violation of one automatically leads to violation of the other. They impart a direction for making the energy transformation a possibility. Let us take up for the sake of illustration, the following examples of isolated systems:

(1) Free expansion: The free expansion of an ideal gas from a region of high pressure to a region of low pressure takes place spontaneously until the pressure becomes uniform. 

(2) Heat conduction: The passage of heat form a region of high temperature to the region of low temperature takes place spontaneously until the temperature becomes uniform. 

(3) Diffusion: The diffusion of a solute from a region of high concentration to a region of low.

Thus, one can conclude that every system, if left to itself (isolated), changes spontaneously at concentration takes place spontaneously until concentration becomes uniform. slow or rapid rate in such a way as to approach a definite final state of equilibrium, In such processes, according to first law of thermodynamics, the total energy of the system involved remains constant before and after the change. The important point to note in these processes is the direction e.g., from high pressure to low pressure, from high temperature to low temperature There is, thus, a direction which allows a system to come to equilibrium. However, if we imagine that after acquiring equilibrium the process is reversed then obviously the system, at its own, will not move away from the state of equilibrium unless aided by some external agency e.g., two bodies at the same temperature, being in a state of thermal equilibrium will themselves not create temperature difference between them provided one of them is not heated by some external source. This principle which determines the direction for the process to take place is second law of thermodynamics. For the first law it does not matter how the equilibrium has been attained because before and after the equilibrium state, energy of the system remains the same. Therefore, second law of thermodynamics cannot be derived from first law. It requires another thermodynamical parameter for description and mathematical formulation. This parameter is entropy.

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