Reversible and Irriversible process lecture two

Reversible process: 

I wrote the definition on first lecture. You can check here. 

Q. Write down the conditions for reversibility for any heat engine .

Answer:    1. The pressure and temperature of the working substance must not differ appreciably from those of the surrounding at any stage of the cycle of operation. 

2. All the process taking place in the cycle of operation must be infinitely slow.

3. The working parts of the engine must be completely free form friction.

4. There should not be any loss of energy due to conduction, convection or radiation during the cycle of operation.

5. The reversible process is not spontaneous.

6. This process will return with same energy.

Q. Why all changes in nature are all irreversible?

Answer:

 1. The conditions for thermodynamic equilibrium i.e. mechanical, thermal or chemical equilibrium are not satisfied because a natural process does not take place quasi-statically.

2. Dissipative effect, such as friction, viscosity, in-elasticity, electric resistance, eddy formation etc. are always present.

Example: spontaneous expansion of a gas in to an evacuated space, spontaneous conduction of heat along a metal bar which is hot at one end and cold at the other, transfer of heat by radiation from hotter body to a cooler body, transfer of electricity through a resistor.