Define the spontaneous processes with example

Spontaneous processes:
A spontaneous process is one in which heat is transferred through a finite temperature. Spontaneous process is also known as irreversible process because these processes take place at very fast rate. All the natural processes are spontaneous processes.

Examples of irreversible processes are as follows:

1) Relative motion with friction
2) Falling of the water from the hill
3) Electricity flow through a resistance.
4) Throttling process
5) Plastic deformation

Irreversible processes are of two types:
1) External irreversibility:
These are associated with dissipating effects outside the working fluid.
For example: mechanical friction occurring during the process due to some external source.

2. Internal irreversibility:
These are associated with dissipating effects within the working fluid.
For example: Unrestricted expansion of the gas, viscosity and inertia of the gas.