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Reversible process in thermodynamics

The process is called reversible process which can run back reversely with the same quantity of heat goes forward process. Forward heat and work done is equal with reverse heat quantity and work done.  There is no loss in reversible process.

reversible process

Figure: Reversible process

Suppose, the executive material of a system undergoes A to B state shown in figure. Imagine the executive material takes Q heat and does W work. In thermodynamics this is known as direct process. When the material substance goes back B to A state at the same environment called reverse process. If the material substance releases same quantity heat Q and does same work W to the material then the whole process is called reversible process. Change of entropy in reversible process is zero.

Examples of reversible process

  1. i) Ice converts into water taking certain amount of heat. And same water converts into ice releasing same amount of heat. So it is reversible process.
  2. ii) Suppose a cylinder piston can move friction less. Take some gas in the cylinder. Compress the volume of the gas in isothermal process so work has done. If we let the gas to work against the piston it goes back previous position, again same work done occurs. In that case we can say the whole process is reversible process.

Condition of reversible process

Two major condition of reversible process are

  1.  Condition change of the process should be very slow
  2.  Dissipation or waste will not happen in this process

but practically these two conditions maintenance very difficult. So reversible process is an ideal imaginary process which not really possible.

Irreversible process

Irreversible process is that process which does not go back at forward process.

All natural process is irreversible process. Entropy change of irreversible process is positive.

irreversible process

Figure: Irreversible process

Examples of irreversible process

  1. Flowing of current through resistance induces heat that is an irreversible process.
  2. Production of heat cause of friction is irreversible process. Because produced heat cannot be converted into work done again.

3. if two different types of substance having different temperature one has high temperature and another is low temperature connects each other, heat goes from high to low temperature.  But heat does not flow from low temperature to high temperature substance. It is an irreversible process.

Distinction between reversible and irreversible processes

Reversible process

  1. Reversible process goes backward. Same amount heat and work done occur both forward and back3.ward time.
  2. It is a slow process.
  3. It is not spontaneous process.
  4. Executive material goes back at primary condition.
  5. This process is dissipation free process.

Irreversible process

  1. Irreversible process cannot move backward.
  2. It is a fast process.
  3. It is spontaneous process.
  4. Executive material cannot go back at primary condition.
  5. This process is not dissipation free process. Wastage occurs.