These are chemical reactions showing the conversion of elements and compounds:

1) Iron $Fe$ is oxidized to form Iron$III$ oxide $F{e}_2{O}_3$, which then reacts with hydrochloric acid to form Iron$III$ chloride $FeC{l}_3$, and finally forms Iron$III$ hydroxide $Fe(OH{)}_3$ in a precipitation reaction.

2) Aluminum $Al$ reacts with chlorine gas to form Aluminum chloride $AlC{l}_3$, which then reacts with water to form Aluminum hydroxide $Al(OH{)}_3$, and finally dehydrates to form Aluminum oxide $A{l}_2{O}_3$.

3) Sulfur $S$ undergoes oxidation to form Sulfur dioxide $S{O}_2$, which further reacts with oxygen to form Sulfur trioxide $S{O}_3$, then reacts with water to form Sulfuric acid $H_{2}S{O}_4$, and finally reacts with Barium chloride to form Barium sulfate $BaS{O}_4$ in a precipitation reaction.