Limiting reactant and Percentage conversion

Limiting reactant

• The reactant that first disappears as reaction proceeds is called as limiting reactant.
• The limiting reactant is always present in less than its stoichiometric proportion with respect to other reactant components.

Excess reactant

• This reactant present in excess than the theoretical or stoichiometric requirement.

 For example, consider reaction, production of ethylene oxide

C2H4 + 1/2 O2 → C2H4O

•  For the production of ethylene oxide, by oxidation of ethylene. the oxygen fed to the reactor always in excess of theoretical requirement
• Hence ethylene is a limiting reactant and oxygen is an excess reactant
• But when reactants are present in stoichiometric proportion then none of the reactants involved is limiting.

Percentage conversion

• The conversion is based on limiting reactant.
• From percentage conversion, we can find out a degree of completion of the reaction.

For example

 A + B → C

 Where A is limiting reactant and B is an excess reactant