👉 Molecularity is a concept in chemistry that refers to the number of atoms or molecules per unit volume. It is often used in the context of gas phase reactions, where it indicates the size of the molecule involved in the reaction. For example, if a reaction takes place in an ideal gas (i.e., no external pressure), the molecularity would be one as there are only two types of atoms or molecules present - hydrogen and oxygen. If the reaction occurs at high pressure (in a sealed