Make the equations H2S ← S → FeS → H2S ↓ Na2S

1. The reaction of incomplete oxidation of hydrogen sulfide when passing in a furnace over the catalyst bed:

2H2S + O2 = 2H2O + 2S.

2. Obtaining iron (II) sulfide in the course of the reaction of iron and sulfur:

Fe + S = FeS.

3. Decomposition of sulfide when interacting with hydrochloric acid into hydrogen sulfide and salt:

FeS + 2HCl = FeCl2 + H2S.

4. Reaction of a weak acid with an excess of alkali:

H2S + 2NaOH = Na2S + 2H2O.