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

$N_2+3H_2\to 2N{H}_3$ $N_2+3H_2\to 2N{H}_3$

$2Al+3S\to A{l}_2{S}_3$

$2Fe+3C{l}_2\to 2FeC{l}_3$

$FeO+Hg\to HgO+Fe$

$2HgO\to 2Hg+O_2$