Definition of path function:-

                                          The thermodynamic property of a system which not depends upon initial and final state and depends upon the path followed by the system is known as path function.

The thermodynamic property which is not state function then this is called path function           

Thermodynamics equilibrium:-

                             The system is said to be in thermodynamics equilibrium when state function of the system do not change with time.

Process and types of processes

 Process: - Transition from one equilibrium state to another is called process.

Isothermal Process :- ( Iso = Same, Thermal = Temperature.)

                            The process in which the temperature of the system remains constant throughout the transformation is known as isothermal process.

                                    In isothermal process   T₁ = T₂

          ΔT =T₁ –T₂

          ΔT = 0(Zero) , ∆U =0

Isobaric process :- ( Iso = Same, Baric = Pressure)

                                  The process in which the pressures of the system remain constant throughout the change is known as isobaric process.

                                    In isobaric process   P₁ = P₂

          ΔP =P₁ –P₂

          ΔP = 0(Zero)

Isochoric process :- ( Iso = Same, Choric = Volume)

                               The process in which the volumes of the system remain constant throughout the change is known as isochoric process.

                                    In isochoric  process   V₁ = V₂

          ΔV =V₁ –V₂

          ΔV = 0(Zero)

Adiabatic process:-

                     The process in which there is no exchange of heat between system and its surrounding known as adiabatic process.

                                    In adiabatic process   q=0 

Reversible process:-

                                    It is very slow process in which driving force and opposing force is nearly equal and difference between  this two are very –very small.

                                                                   OR

                                    Any process conducted in such a manner that at every stage the driving force is only infinitesimally greater than opposing force and which can be reversed by slight increase in opposing force is called Reversible Process.

                                            Driving force >~ Opposing force 

Example: -   Slow expansion of ideal gas in cylinder fitted with weight less friction less piston. 

 Feature of reversible process –

1             *      Driving and opposing forces are only infinitesimally different from each other

2             *    The process can be reversed at any point during the process by making infinitesimal                    change in condition.

            *    The process takes place in an infinite number of step

                *      Maximum work is obtained during a reversible process 

Difference between isothermal and adiabatic processes-

Isothermal process	Adiabatic process
In this process temperature remain constant.	In this process temperature may be increases or decreases
Internal energy remain constant. ΔU = O	Internal energy is varies ΔU # O
The maximum work is obtain	The maximum work done is not obtain
For isothermal process q = -W	For adiabatic process q +W =∆U
The system is not thermally isolated from its surrounding hence either open or closed System is required	The system is thermally isolated from its surrounding hence isolated System is required
System can exchange heat with surrounding	System cannot exchange heat with surrounding
Example:-  isothermal expansion of an ideal gas	Example:- Adiabatic expansion of an ideal gas