Definitions
Heating enthalpy of solids

When a quantity of heat ΔQ is received by a system and causes a temperature change ΔT = T₁ – T₂ (with T₁ and T₂ , respectively the start and end temperatures of heating), the average heat capacity C of the system of mass m is written :

provided the system undergoes neither reaction nor first-order transition in the Ehrenfest sense (enthalpy and entropy discontinuities) between T₁ and T₂ , i.e. heat exchanges with the outside have the exclusive effect of raising the temperature of the system (neither heat of reaction nor enthalpy of change of state).

The limiting value of C when ΔT tends towards zero is...