Thermal Ionization of a Monatomic Gas

One interesting application of Nernst’s equation was made by Dr. M.N. Saha to the thermal ionization of a monatomic gas. If a monatomic gas is heated to a high enough temperature (5000 K and above), some ionization occurs, with the electrons in the outermost orbit being shed off, and the atoms, ions, and electrons may be regarded as a mixture of three ideal monatomic gases, undergoing the reaction

(3.65)

Starting with n₀ moles of atoms,

The equilibrium constant is given by

(3.66)

or,

(3.67)

Since the three gases are monatomic, which, on being substituted in the Nernst’s equation, gives

(3.68)

where                                     

Now,

(3.69)

∴

(3.70)