what volume of hydrogen sulfide is produced by reaction of 0.5 mole of sodium sulfide with hydrochloric acid at a temp. of 20C and a pressure of 722 mm.

Answer 1

Na2S + 2HCl ==> H2S + 2NaCl
mols Na2S = 0.5
From the equation you see it produces 1 mol H2S for 1 mol Na2S; therefore, you should obtain 0.5 mol H2S.
Use PV = nRT, substitute the conditions and solve for V.