Basics of Materials Balance

Law of conservation of Mass

Mass of isolated systems remains constants irrespective of the changes occurring within the system. Consider an open system of constant volume &  mass.

Mass is transferred in to and out of the system; mass will accumulate if transfer rates are unequal Material balance at unsteady state is

= +

(1)

(2)

Material balance equation is written for each component involved in the process;

(3)

For a systems with multiple input and output streams, the material balance equation for Ith component

(4)

                                                                                                            
For steady state

(5)

                                                                          
For chemically reacting systems  in addition to the law of conservation of mass, following two laws must also hold:

1.   Law of definite proportions:

A given chemical compound always   contains the same constitute elements in the same weight proportions. True for stoichiometric compounds.

2.   Law of multiple proportions:

If two elements can form more than one compound, then the respective weights of one element that combines with a given weight of the other are in the ratio small whole numbers.