https://doi.org/10.1351/goldbook.H02753
Heat brought to a system to increase its temperature divided by that temperature increase. At constant volume \(C_{V}=(\frac{\partial U}{\partial T})_{V}\) at constant pressure \(C_{p}=(\frac{\partial H}{\partial T})_{p}\), where \(U\) is the @[email protected] and \(H\) the @[email protected] of the system.