[Gold]

How many Kilograms of hydrogen sulfide can be prepared by treating 400 g of iron(II) sulfide with an excess of hydrochloric acid?
FeS(s) + HCl(aq) -> FeCl2(aq) + H2S(g) (unbalanced)

This is the question and formula I was given, but I do not know what they mean by an "excess" of hydrochloric acid and do I balance or leave it the way it is?

[Schrödinger]

Excess of hydrochloric acid means that FeS is the limiting reactant. i.e., you don't have to worry about the amount of HCl present in the reaction mixture