The ideal gas equation is an equation, which relates all the properties of an ideal gas. An ideal gas obeys Boyle’s law and Charles’s law and Avogadro’s law. 

According to Boyle’s law, 

PV = constant ………. (1) 

According to Charles’s law,

\(\frac{V}{T}\) = constant …… (2)

According to Avogadro’s law,

\(\frac{V}{T}\) = constant  .….. (3)

After combining equations (1), (2) and (3), you equation. can get the following

\(\frac{V}{nT}\) = constant ….. (4)

The above relation is called the combined law of gases. If you consider a gas, which contains µ moles of the gas, the number of atoms contained will be equal to µ times the Avogadro number, N₀.

I.e., n = μN_A

Using equation (5), in equation (4) can be written as

\(\frac{PV}{μ N_AT}\) = constant

The value of the constant in the above equation is taken to be K_B, which is called as Boltzmann constant (1.38 × 10^-23 JK^-1). Hence, we have the following equation:

\(\frac{PV}{μ N_AT}\) = K_B

PV = µN_A K_B T

µN_AK_B = R

which is termed as universal gas constant whose value is 8.31 J mol^-1 K^-1.

PV = RT

Ideal gas equation is also called as equation of state because it gives the relation between the state variables and it is used to describe the state of any gas.