Consider this reaction:
h2 (g) + cl2 (g) → 2 hcl (g)
how many liters of hcl are produced when 56 l of chlorine are reacted with excess
hydrogen?
(one mole of any gas occupies 22.4 l under certain conditions of temperature and
pressure. assume those conditions for this question.)
a. 22.4l
b. 56 l
c. 112
d. 224 l

Explanation:

We can use Avogadro's Law: Equal volumes of gases under the same conditions of temperature and pressure contain the same number of molecules.  

To say it another say, gases react in the same volume ratios as their coefficients in the balanced equation.

  H₂  +    Cl₂  ⟶ 2HCl

1 mol + 1 mol ⟶ 2 mol

  1 L  +   1 L    ⟶   2 L

Thus,