In the case of a solid possessing a small expansion coefficient,

The general thermodynamic relation between the molar heat capacities at constant pressure ($C_p$) and constant volume ($C_V$) is given by:

$C_p - C_V = \dfrac{T V \alpha^2}{\beta}$

where $T$ is the absolute temperature, $V$ is the molar volume, $\alpha$ is the coefficient of volume expansion, and $\beta$ is the isothermal compressibility.

For any substance, $T$, $V$, and $\beta$ are positive quantities. Since the term $\alpha^2$ is always positive, it follows that $C_p - C_V > 0$, meaning $C_p > C_V$.

For a solid with a small expansion coefficient ($\alpha$), the term $\alpha^2$ is very small. Consequently, the difference $C_p - C_V$ is a small positive value.

Therefore, $C_p$ is slightly greater than $C_V$.