$2Mg+O_2\to 2MgO$

$2H_2+O_2\to 2H_{2}O$

$Mg+C{l}_2\to MgC{l}_2$

$H_2+C{l}_2\to 2HCl$

$C+O_2\to C{O}_2$

$F{e}_2{O}_3+3H_2\to 2Fe+3H_{2}O$