Physics – 2.2.1 Thermal expansion of solids, liquids and gases | e-Consult

As the temperature of a substance increases, the kinetic energy of its constituent particles (atoms or molecules) also increases. This increased kinetic energy affects the motion and arrangement of the particles differently in solids, liquids, and gases, leading to varying degrees of expansion.

Solids: In solids, particles are tightly packed in a fixed, regular arrangement. They vibrate about their fixed positions. As the temperature rises, the particles vibrate with greater amplitude. However, due to the strong intermolecular forces holding them in place, the increase in vibrational energy is largely manifested as an increase in the amplitude of these vibrations, resulting in a relatively small change in the average separation between particles. Therefore, solids experience a small degree of expansion.

Liquids: In liquids, particles are still close together but have more freedom of movement than in solids. They can slide past each other. When the temperature increases, the particles gain kinetic energy and move more rapidly and further apart. The increased kinetic energy overcomes some of the intermolecular forces, leading to a greater average separation between particles compared to solids. This results in a moderate degree of expansion.

Gases: In gases, particles are widely separated and move randomly. The intermolecular forces are very weak. As the temperature increases, the particles gain significant kinetic energy and move much faster and with greater force. This results in a substantial increase in the average distance between particles and a significant expansion of the gas. The increased motion and greater separation of particles lead to a large degree of expansion.

In summary, the relative order of magnitudes of expansion is: Gases > Liquids > Solids. This is directly related to the degree of freedom of movement and the strength of intermolecular forces. Gases have the most freedom and weakest forces, leading to the largest expansion, while solids have the least freedom and strongest forces, resulting in the smallest expansion.