When barium chloride combines with sodium sulphate in the form of their aqueous solutions, a white precipitate of barium sulphate is formed which is insoluble in water. The reaction also creates sodium chloride, which remains dissolved in water and so cannot be seen. Here, the products formed are entirely different from the reactants in chemical composition and chemical properties. So this reaction is a chemical change.
This video explains the chemical change occurs during the reaction between sodium sulphate and barium chloride.