Material Balance

What is Material Balance?

        A material balance is also known as Mass Balance. It is an application of conversation of mass to the analysis of physical system.

         By accounting for the material entering and leaving a system, mass flows can be identified which might have been unknown, or difficult to measure.


                     Total Mass Entering the unit = Total mass of Product leaving the unit

Material Balance Without Chemical Reaction
 
        The Mass balance for a system without a chemical reaction is as follows,

                  Input = Output + Accumulation

         In the absence of a chemical reaction the amount of any chemical species flowing in and out will be the same.


Material Balance With Chemical Reaction 

       Generally some kind of chemical reaction takes place in most of the sections in a manufacturing industry and we need to calculate the overall efficiency or section - wise process efficiency. This can be carrying out the section wise or overall material balance. Therefore we define some useful terms related to this concept.


Stoichiometry
     
      It is a theory of the proportions in which chemical species combine with one another.


Stoichiometric Co-efficient 

     It is the number that precedes the formula of each component involved in a chemical reaction.


Stoichiometric Ratio 
 
     Two reactants A and B are said to be present in stoichiometric proportions if the ratio of moles of A present to the moles of B present is equal to the stoichiometric ratio obtained from the balanced equation.


Limiting of Excess Reactant 

    In most the chemical reaction, two or more components are involved and they are generally not in their stoichiometrically required ratios due to technical, economical or safety reasons. The one which is in less quantity  is decided by stoichiometric coefficient, is known as limiting reactant. The one which is in excess quantity is known as excess reactant.


Conversion
   It is defined as the ratio of the reacted amount of a component to its initial amount. It can be expressed as mole%, volume% or mass%.


Yield 

   It is defined as the ratio of actual amount of the product formed to the theoretically calculated amount of the product as per the reaction.


Selectivity

  It is also used to measure the proportion of the total reaction which produces the desired product. It is defined as the ratio of amount of limiting reactant reacted to give desired product to the amount of the same reactant reacted to give undesired product.