Which of the processes described below are irreversible? - Vidyadip

MCQ

Which of the processes described below are irreversible?

A
The increase in temprature of an iron rod by hammering it.
B
A gas in a small cantainer at a temprature T₁ is brought in contact with a big reservoir at a higher temprature T₂ which increases the temprature of the gas.
C
A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston.
D
An ideal gas is enclosed in a piston cylinder arrangement with adiabatic walls. A weight W is added to the piston, resulting in compression of gas.

✓

Answer

The increase in temprature of an iron rod by hammering it.
A gas in a small cantainer at a temprature T₁ is brought in contact with a big reservoir at a higher temprature T₂ which increases the temprature of the gas.
A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston

Explanation:

Key concept: Reversible process: A reversible process is one which can be reversed in such a way that all changes occurring in the direct process are exactly repeated in the opposite order and inverse sense and no change is left in any of the bodies taking part in the process or in the surroundings.
The conditions for reversibility are:

There must be complete absence of dissipative forces such as friction, viscosity, electric resistance etc. ~
The direct and reverse processes must take place infinitely slowly.
The temperature of the system must not differ appreciably from its surroundings.

Irreversible process: Any process which is not reversible exactly is an irreversible process. All natural processes such as conduction, radiation, radioactive decay etc. are irreversible. All practical processes such as free expansion, Joule-Thomson expansion, electrical heating of a wire are also irreversible.

In this case internal energy of the rod is increased from external work done by hammer which in turn increases its temperature. So, the process cannot be retraced itself.
In this process energy in the form of heat is transferred to the gas in the small container by big reservoir at temperature T
In a quasi-static isothermal expansion, the gas is ideal, this process is reversible because the cylinder is fitted with frictionless piston.
As the weight is added to the cylinder arrangement in the form of external pressure hence, it cannot be reversed back itself.

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