What is the Zeroth Law of Thermodynamics What is an ideal gas What is the difference between universal gas constant and characteristic gas constant

zeroth law of thermodynamics:

"when two bodies or system are in thermal equilibrium with third body then they are thermal equilibrium with each other."
                                        IF,      A=B,
                                                  C=B,
                                      THEN,
                                                  A=C 
Applications of Zeroth law:
1.Principle of thermometry:
                       In Thermometry, a property which vary with respect to temperature is found first and with the help of this property unknown temperature can be found.

  Ideal gas:

            Gas said to be a ideal gas whaen molecular forces are zero. For every gas having pressure <10 kpa,and temperature very very high then it considered as ideal gas.

           A gas which obeys ideal gas equations at all pressure, temperature, and volume is know as ideal gas.

                                      PV=MRT

WHERE,

P=absolute pressure in kpa.

v=volume in metercube

m=mass in kg

T=absolute temperature in degree kelvin

R=characteristics gas constant in kJ/kg-degree kelvin 

Difference between universal gas constant and characteristic gas constant :

while solving numericals of thermodynamics we use either characteristics or univarsal gas constant 

universal gas constant 

 _{Accourding to Avargadro hypothesis,"At particular pressure, temperature and volume every gas have same numbers of moles."}

                              _MR=R_u

                          R_u=universal gas constant 

                            =8.314 KJ/kmole.K

                       P V=n R_u T

Characteristic gas constant 

When the equation deals with mass, the characteristic gas constant (R) is used. It is a gas constant per unit mass and it is different for different gases. As such

                                                                          R_u=MR

          where,

                   R=0.287 kJ/kgK (for air having molecular weight (M)=29)