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

Definition of state function:-

                                                The thermodynamic property of a system which is depend upon initial and final state and does not depend upon the path followed by the system is known as state function. Example: - Temperature, pressure, volume.

Explain internal energy is a State Function

 Internal energy:-

                        The sum of all form of energy associated with matter present in the system is called internal energy of a system. 

SOLUTION :

                            Consider system A having Internal energy U₁ , pressure P₁ and Volume V₁ ( initial state ) and system B having Internal energy U₂ , pressure P₂ and Volume V₂ ( final state )Suppose that change in state A to state B along Path I.

             

           Change in internal energy along path A is (pathI)

                        ΔU (path I) =  U₂  - U₁

     Again consider that change in state B to State A along path II

             Change in internal energy along path B is (pathII)

                        ΔU(path II) =  U_{1 -} U₂

                        ΔU = ΔU (path I) + ΔU( path II )

                         ΔU    = (U₂  - U₁ ) +( U_{1 -} U₂ )

ΔU    = (U₂ - U₂) + (U₁ - U₁ )

                          ΔU    =   0

From the above equation we can say that internal energy is state function.

Concept in thermodynamics

System:
        The system may be defined as any specific portion of universe which is chosen to study the thermodynamics’ properties.
Example:
  1) Open vessel containing boiling water
  2) Wooden box which is used in physical experiment

Surroundings:
        All other part of universe other than system where observation is made known as surrounding.

Boundary:
        The real and imaginary out line which separates the system from surrounding is known as boundary.

Types of system:-
1) Open system
2) Closed system
3) Isolated system 

1)Open system :-
                     The system in which exchange both matter as well as energy with its surrounding is known as open system.
   
Example:-
1)    Open vessel’s containing water.
2)    Cup of tea 

2) Closed system:-                       

               The system which can exchange only energy but not matter with its surrounding is known as closed system.  Here the energy is either gained or loss by the system with surrounding but does not exchange matter.

            Example: - closed vessel containing boiling water 

3) Isolated system:-

                        The system cannot exchange either matter or energy (heat) with its surrounding is called isolated system. 

Example: - Hot water in thermos

Property of system:-    

 Property of system are generally classified into two type

1)     Extensive property

2)     Intensive property 

Extensive property:-

                   The property of system whose magnitude depends upon the quantity of matter present in the system is known as extensive property.

Example: -

1)       Mass   2) Volume 3) Energy. 4) Heat capacities 5) Number of moles

Intensive property:-

             The property of system whose magnitude is independent of the quantity of matter present in the system is known as Intensive property.

Example:-

1)     Temperature.    2) Density   3) Melting point 4) Viscosity 5) Refractive index 

6) Melting point

 State variable;

                         Every system has a certain measurable thermodynamics properties such as temp. Pressure and volume this property are state variable.

State of system: -

           State of system is defined by specifying the values of state variable like temp. Pressure, volume etc

                   If any one of these property changed then there will be change in a state of system.