Molarity and molecularity are two distinct concepts in chemistry:
Molarity: Molarity, symbolized as M, is a measure of the concentration of a solute in a solution. It is defined as the number of moles of solute per liter of solution. Molarity is calculated by dividing the number of moles of solute by the volume of the solution in liters. Molarity is commonly used to express the concentration of substances in various chemical reactions and is widely employed in stoichiometry calculations.
Molecularity: Molecularity refers to the number of molecules that participate as reactants in an elementary reaction (a reaction that occurs in a single step). It is a concept used in the field of reaction kinetics to describe the mechanism of a chemical reaction. Molecularity is determined experimentally and cannot be deduced from the balanced chemical equation. The molecularity of a reaction can be unimolecular (one molecule), bimolecular (two molecules), or termolecular (three molecules) depending on the number of reactant molecules involved in the elementary step.
In summary, molarity relates to the concentration of a solute in a solution, while molecularity pertains to the number of molecules involved in an elementary reaction step.