2.2 The first law 1). The internal energy The internal energy, U: the total energy of a system is called its internal energy; it is the total kinetic and potential energy of the molecules composing the system The internal energy is a state function. It is a extensive property. Internal energy, heat, and work are measured in the same units, the Joule(j). 版权所有:华东理工大学物理化学教研室版权所有：华东理工大学物理化学教研室 10 The internal energy, U : the total energy of a system is called its internal energy;it is the total kinetic and potential energy of the molecules composing the system. The internal energy is a state function. It is a extensive property. Internal energy, heat, and work are measured in the same units, the Joule (J). 2.2 The First Law 1). The internal energy