System And Surroundings

System

The matter which is being studied in thermodynamics is known as system.

Surroundings

Everything external to system is known as surroundings.

In thermodynamics generally we concentrate over the system. System and surroundings are separated by boundaries.

State of the system

A system is said to be at a particular state when all the properties of a system are well defined at that time.

Change of state

During any operation, if one or more properties of the system changes then this is called change of state and the path followed by the system during this change is called path of change of state.

Fig. System and Surrounding

Process

When during any operation path of change of state is completely specified then it is called a process. These are of four types.

1. Cyclic Process

2. Quasis-static Process

3. Reversible Process

4. Irreversible Process

1. Cyclic Process – A process is said to be cyclic process if it undergoes a process or number of process such that the value of all properties at the end are equal to the value at the start.

2. Quasis-static Process – A process is said to be quasis-static process if it undergoes through a state of equilibrium states. Such that the path of change of state is well defined. Very slow is the characteristic of the quasis-static process.

3. Reversible Process – A process is said to be reversible process if it undergoes through a series of equilibrium states. If reversible process makes move in backward direction then it should retrace the same path as is traced during the forward movement. When system reaches to its original position then no effect on the surrounding should be remained. Example Frictionless motion and elastic deformation.

Conditions for reversible process.

a) Motion in the absence of friction.

b) Process should be Quasis-static.

c) Heat transfer must be through infinitely small temperature difference.

4. Irreversible Process – A process is said to be irreversible process if it undergoes through a series of non equilibrium state such that path of state of change is unknown to us.

An irreversible process when work in the backward direction it does not traces its original path. It is impossible to draw irreversible process on any co-ordinate system because of presence of non equilibrium states during change of state. Example motion in the presence of friction, Plastic deformation, mixing of sugar in milk.

Conditions for reversible process.

a) Presence of friction

b) Heat transfer through a finite difference

c) Mixing of fluid