Basic Definitions of thermodynamics

1. What is Thermodynamics ?
Ans. It is branch of physics concerns  with heat and temperature and having relations with the energy and work .

2. What is difference between heat and temperature?
Ans.                       HEAT
It is a form of energy and it measures the total energy of molecules of the substance which is the sum of kinetic energy and potential energy.
It's SI unit is joule and calorie in cgs unit.
                    
                                  TEMPERATURE
It is measure of  degree of hotness and coldness of a body which is the average kinetic energy of the molecules of the body .
It's unit is degree centigrade and degree Fahrenheit.

3. What is Zeroth law of thermodynamics
Ans. When two thermodynamic system each is in thermal equilibrium with third  system then they are in thermal equilibrium with each other .

4. What is difference between Entropy and Enthalpy ?
Ans.                            Entropy
It is the measure of molecular disorder and randomness of the system which is the unavailable energy for unit temperature for doing useful work .

Useful work can be taken from ordered molecules only.

It is an example of  extensive property .

It's SI unit is joule /Kelvin.

Mathematically expressed as
                                dS =dQ/dT
                            
                                    Enthalpy
It is the sum of internal energy and product of pressure and volume of thermodynamic system .

Mathematically,
                                   H = E + PV
It's SI unit is joule .
It is equivalent to total heat content of the system.

It is an example of extensive property.

Q.5 What is difference between extensive and intensive property with examples ?
Ans.                   Extensive property
It is the property which depends upon the size and mass of the system .
Eg. Pressure ,volume ,  Enthalpy ,entropy ,  internal energy etc.
                          Intensive property
It is the property which is independent of mass and size of the system .
Eg. Density , boiling temperature, freezing point ,temperature

Extensive property can be changed into intensive property just by dividing it by mass .
Eg . Specific volume (m^3/kg), specific entropy (j/kg.k), specific Enthalpy (j/kg)

INtensive means INdependent for remembering it .