The Neumann-Kopp law is a generalized experimental finding that the heat capacity of a substance can be well approximated by the sum of the heat capacities of the constituent elements, weighted by their contribution to the total composition. For example, a generic salt represented by M2X5 would have a molar heat capacity close to 2CV,m(M)+5CV,m(X), where M and X are both solids. Provide a reasonable theoritical explanation for the Neumann-Kopp law.