The preparation of 2,4-dichloronitrobenzene from nitrobenzene and chlorine gas involves an electrophilic aromatic substitution reaction. The balanced chemical equation for this reaction is:C6H5NO2 + 2 Cl2 C6H3Cl2NO2 + 2 HClNitrobenzene C6H5NO2 reacts with chlorine gas Cl2 to form 2,4-dichloronitrobenzene C6H3Cl2NO2 and hydrogen chloride HCl .