If the final particles after collision is entirely different from the initial particles before collision, then this type of collision is known as reaction. The initial particles are known as reactants and the final particles are known as the products.

Since the interacting particles are isolated and no external torque acts on the system so in this process the linear momentum and the angular momentum are conserved but the sum of the kinetic energies of the colliding particles after collision is not same as the sum of the kinetic energies of those colliding particles before collision.