H2O + Cl2 + H2SO3 = H2SO4 + HCl

H_2O (water) + Cl_2 (chlorine) + H_2SO_3 (sulfurous acid) ⟶ H_2SO_4 (sulfuric acid) + HCl (hydrogen chloride)

Balance the chemical equation algebraically: H_2O + Cl_2 + H_2SO_3 ⟶ H_2SO_4 + HCl Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2O + c_2 Cl_2 + c_3 H_2SO_3 ⟶ c_4 H_2SO_4 + c_5 HCl Set the number of atoms in the reactants equal to the number of atoms in the products for H, O, Cl and S: H: | 2 c_1 + 2 c_3 = 2 c_4 + c_5 O: | c_1 + 3 c_3 = 4 c_4 Cl: | 2 c_2 = c_5 S: | c_3 = c_4 Since the coefficients are relative quantities and underdetermined, choose a coefficient to set arbitrarily. To keep the coefficients small, the arbitrary value is ordinarily one. For instance, set c_1 = 1 and solve the system of equations for the remaining coefficients: c_1 = 1 c_2 = 1 c_3 = 1 c_4 = 1 c_5 = 2 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | H_2O + Cl_2 + H_2SO_3 ⟶ H_2SO_4 + 2 HCl