Final answer:
Substitution in chemistry refers to a reaction where one or more atoms or groups of atoms replace another atom or group of atoms in a molecule. It can occur in various types of reactions, such as the substitution of a halogen atom for a hydrogen atom in alkyl halides.
Step-by-step explanation:
In chemistry, substitution refers to a reaction where one or more atoms or groups of atoms replace another atom or group of atoms in a molecule. This can happen in various types of reactions, such as the substitution of a halogen atom for a hydrogen atom in alkyl halides. An example of a substitution reaction is the reaction between ethane and molecular chlorine, where a hydrogen atom in ethane is replaced by a chlorine atom:
CH3CH3 + Cl2 → CH3CH2Cl + HCl