Understanding the Fundamental Laws of Gases: Boyle's, Charles's, and Avogadro's Law

Fundamental Laws of Gases

This post provides study material, lecturing notes, and a detailed explanation of the fundamental laws governing gases in thermal physics.

Introduction to Gas Laws

The three fundamental laws which connect the relation between pressure, volume and temperature are as follows:

1. Boyle’s Law
2. Charles's law
3. Avogadro's law

1. Boyle’s law:

When the temperature of a gas is kept constant, the volume of a fixed mass of gas is inversely proportional to its pressure. This is shown in Figure 3.6.

\( P \propto \frac{1}{V} \)

Figure 3.6 Variation of volume with pressure

In other words, for an invariable mass of a perfect gas, at constant temperature, the product of its pressure and volume is a constant.

\( PV = \text{constant} \)

2. Charles's law (The law of volume)

Charles’s law was formulated by a French scientist Jacques Charles. According to this law, When the pressure of gas is kept constant, the volume of a gas is directly proportional to the temperature of the gas.

\( V \propto T \)

or

\( \frac{V}{T} = \text{constant} \)

3. Avogadro's law

Avogadro's law states that at constant pressure and temperature, the volume of a gas is directly proportional to number of atoms or molecules present in it.

i.e. \( V \propto n \)

(or)

\( \frac{V}{n} = \text{constant} \)

Avogadro’s number (\(N_A\)) is the total number of atoms per mole of the substance. It is equal to \(6.023 \times 10^{23}\) /mol.