The balanced chemical equation for the preparation of 2,4-dichlorobenzoic acid via the reaction between benzoic acid and chlorine gas under specific reaction conditions UV light or a catalyst like FeCl3 is:C6H5COOH + 2 Cl2 C6H3Cl2COOH + 2 HClBenzoic acid reacts with chlorine gas in the presence of UV light or a catalyst like FeCl3 to form 2,4-dichlorobenzoic acid and hydrogen chloride.