a,
$Cl_2+H_2O\rightleftharpoons HCl+HClO$
b,
$NaOH+HCl\to NaCl+H_2O$ (Tính axit)
$MnO_2+4HCl\to MnCl_2+Cl_2$ (Tính khử)
$Fe+2HCl\to FeCl_2+H_2$ (Tính oxi hoá)
c,
$H_2+F_2\to 2HF$
$H_2+Cl_2\buildrel{{as}}\over\to 2HCl$
$H_2+Br_2\buildrel{{t^o}}\over\to 2HBr$
$H_2+I_2\buildrel{{t^o}}\over\rightleftharpoons 2HI$