For ten points, what is this rule whose modern statement holds that the molar heat capacity of a solid element is approximately 3 times the gas constant, named for its two French formulators?
Although this is a gross approximation, it applies with fair accuracy to elements with simple crystal structures over a wide temperature range, but fails at low temperatures since when the quantity it involves tends to zero. Frequently used in the 19th century to determine atomic weights, in its original formulation it stated that a constant equal to approximately 25 Joules per Kelvin moles gives the product of the relative atomic mass and specific heat capacity of a solid element. For ten points, what is this rule whose modern statement holds that the molar heat capacity of a solid element is approximately 3 times the gas constant, named for its two French formulators?
Although this is a gross approximation, it applies with fair accuracy to elements with simple crystal structures over a wide temperature range, but fails at low temperatures since when the quantity it involves tends to zero.
Rule of Dulong and Petit (Accept equivalents, e.g. {Dulong} and {Petit}’s Law, etc.)