In this Chapter, first we derive the macroscopic conservation laws of matter, momentum, energy and angular momentum for a multicomponent system subjected to conservative external forces and in which chemical reactions may occur. Then,the time growth of the macroscopic entropy of the system is derived, showing that it can be expressed as the product between thermodynamic fluxes and their conjugated thermodynamic forces. It should be noted that, as shown in an Appendix, these equations are consequences of the fundamental mechanical laws governing the motions of the constituent particles of the system.