Question

Solids expand on heating because

• A. Kinetic energy of the atoms increases
• B. Potential energy of the atoms increases
• C. Total energy of the atoms increases
• D. The potential energy curve is asymmetric about the equilibrium distance between neighbouring atoms

Answer 1

The correct option is D

The potential energy curve is asymmetric about the equilibrium distance between neighbouring atoms

The expansion of solids can be well understood by potential energy curve for two adjacent atoms in a crystalline solid as a function of their internuclear separation (r).

At ordinary temperature : Each molecule of the solid vibrate about it' s equilibrium position $P_1$ between A and B ($r_0$ is the equilibrium distance of it from some other molecule)

At high temperature : Amplitude of vibration increase (C « D and E « F). Due to asymmetry of the curve, the equilibrium positions ($P_2$ and $P_3$) of molecule displaced. Hence it's distance from other molecule increases ($r_2$ > $r_1$ > $r_0$).

Thus, on raising the temperature, the average equilibrium distance between the molecules increases and the solid as a whole expands.