Solid iron(II) sulfide reacts with aqueous hydrochloric acid HCl to produce hydrogen sulfide gas H2S and aqueous iron(II) chloride . Write a balanced chemical equation for this reaction.

Explanation:

Here translate the words into the atomic symbol:

HCl(aq) + FeS(s) →FeCl2(aq) + H2S(g)

calculation;  

Hydrogens (H); 1 on left, 2 on right

Chloride (Cl);  1 on left, 2 on right

Iron (Fe) ; 1 on left, 1 on right

Sulfur (s);  1 on left, 1 on right

Balancing ; So, need 1 more Hydrogen on the left and 1 more Chloride on the left.  The easiest way to do this is to put a 2 in front of HCl.  

2 HCl(aq) + FeS(s) --->  

Now there are two hydrogens, two chlorides, one iron, and one sulfur on the left and the same on the right.