If there are N  no. of streams going inside a process and M no. of streams coming out of a process, the mass balance equations for the process can be written as:

(II.2)

Where  and V  represent the density and volume of the material inside the system and  and  are the density and flow rate of the incoming/outgoing streams respectively. In case of a chemical reaction, let  and  be the concentrations of component A of material inside the process and the streams respectively and r be the rate of the reaction. The component balance equations can be written as

(II.3)

Let h and  be the enthalpies of material inside the process and incoming/outgoing streams respectively, Q be the heat supplied to the system (or heat removed from the system ), W is the work done on (or by) the system. Then the energy (E) balance equation for such system is written as

(II.4)

As the chemical process plants are usually static, momentum balance equations are usually not required for such cases.

In addition to the above state equations, a few algebraic equations are also useful for modeling of a chemical process. Examples of such equations are:

Transport rate equation:		(II.5a)
Kinetic rate equation:		(II.5b)
Phase equilibrium equation:		(II.5c)
Gas law:		(II.5d)