Kopp's law
# Kopp's law

Kopp's law can refer to either of two relationships discovered by the German chemist Hermann Franz Moritz Kopp (1817–1892).

* Kopp found "that the molecular heat capacity of a solid compound is the sum of the atomic heat capacities of the elements composing it; the elements having atomic heat capacities lower than those required by the Dulong–Petit law retain these lower values in their compounds."
* In studying organic compounds, Kopp found a regular relationship between boiling points and the number of $CH_2$ groups present.

## Kopp–Neumann law

The Kopp–Neumann law, named for Kopp and Franz Ernst Neumann, is a common approach for determining the specific heat C (in $J·kg^{−1}·K^{−1})$ of compounds using the following equation:

$C=\sum _{i=1}^{N}C_{i}f_{i},$

where N is the total number of compound constituents, and $C_i$ and $f_i$ denote the specific heat and mass fraction of the i-th constituent. This law works surprisingly well at room-temperature conditions, but poorly at elevated temperatures.

