Question

Define Ideal Gas

Answer 1

Ideal Gas

An ideal gas or a perfect gas is that gas which strictly obeys the gas laws.

Following are the characteristics of the ideal gas :

• The size of the molecule of a gas is zero, i.e., each molecule of a gas is a point mass with no dimensions.
• There is no force of attraction or repulsion amongst the molecules of the gas.

Equation of an ideal gas : $P V=\mu R T=k_{B} N T$

where $\mu$ is the number of moles and $N$ is the number of molecules, $R$ is the universal gas constant and $k_{B}$ is the Boltzmann constant.

$k_{B}=\frac{R}{N_{A}}$

$N_{A}$ is the Avogadro's number.

Here, $\mu=\frac{m}{M}=\frac{N}{N_{A}}$

where $m$ is the mass of the gas containing $N$ molecules, $M$ is the molar mass.

Another form of an ideal gas equation $P=\frac{\rho R T}{M}$ where $\rho$ is the density of the gas.

Kinetic Theory of An Ideal Gas

According to kinetic theory of an ideal gas pressure exerted by an ideal gas is given by

$P=\frac{1}{3} m n \overline{v^{2}}$

where $n$ is the number density (number of molecules per unit volume), $m$ is the mass of molecule and $\overline{v^{2}}$ is the mean square speed.

Note —

• The internal energy of an ideal gas is equal to its internal kinetic energy, which depends only on the temperature of the ideal gas.
• Average kinetic energy per molecule of a gas depends only on its absolute temperature. It is independent of pressure, volume and nature of the ideal gas.