$Cl_2+ H_2O \rightleftharpoons HCl+ HClO$
$HClO+ HCl \rightarrow Cl_2+ H_2O$
$3Cl_2+ 6NaOH \buildrel{{t^o}}\over\longrightarrow 5NaCl+ NaClO_3+ 3H_2O$
$NaClO_3+ 6HCl \to NaCl+ 3Cl_2+ 3H_2O$
$2NaCl \buildrel{{đpnc}}\over\longrightarrow 2Na+ Cl_2$
$Cl_2+ Ba \to BaCl_2$