The balanced chemical equation for the reaction involving these compounds is:

H2SO3 + SO2 + 2Na2SO3 + 2NaOH -> 3Na2SO4 + 2H2O

In this reaction, sulfur dioxide (SO2) reacts with sodium sulfite (Na2SO3) and sodium hydroxide (NaOH) to form sodium sulfate (Na2SO4) and water (H2O).