Kopp's law

Kopp's law is an empirical rule that a solid compound’s molar heat capacity is approximately the sum of the atomic heat capacities of its constituent elements.

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Heat capacity: The heat transferred to a system per unit increase in its temperature under specified conditions. Kopp's law estimates this bulk thermal property from elemental contributions.
Hermann Franz Moritz Kopp: A German chemist who studied relationships between chemical constitution and physical properties. Kopp formulated the empirical heat-capacity rule bearing his name.
Neumann–Kopp rule: An empirical method for estimating a compound’s heat capacity by summing contributions from its constituent components. It is used to estimate heat capacities of compounds from known component data.
Einstein solid: A model of a crystalline solid that treats its atoms as independent quantum harmonic oscillators with one characteristic frequency. It explains temperature-dependent heat capacity microscopically, unlike Kopp's composition-based empirical sum.
Molar heat capacity: The heat required to raise one mole of a substance by one degree of temperature under specified conditions. The law applies its additivity rule to this quantity.
Pierre Louis Dulong: A French physicist and chemist who investigated the heat capacities of solid elements. His work with Alexis Petit supplied the elemental heat-capacity context for Kopp's rule.
Kirchhoff's law of thermochemistry: A relation stating how a reaction’s enthalpy change varies with temperature according to the heat capacities of reactants and products. Kopp-style estimates can supply heat capacities needed to adjust reaction enthalpies across temperatures.
Debye model: A quantum model of a solid’s heat capacity that represents lattice vibrations with a spectrum of frequencies. It captures low-temperature behavior that Kopp's nearly composition-only rule cannot describe.
Lattice vibration: Collective oscillatory motion of atoms or ions around equilibrium positions in a crystal. These vibrations account for much of a solid’s heat capacity and explain why simple additivity has limits.
Alexis Thérèse Petit: A French physicist who collaborated with Pierre Louis Dulong on the heat capacities of solids. The Dulong–Petit result helped establish the atomic contributions that Kopp later extended to compounds.