When 4.22 moles of Al reacts with 5.0 moles of HBr, how many moles of H2 are formed?

2 Answers
Mar 26, 2016

2.5mol

Explanation:

First write a balanced chemical equation for the reaction of the metal with the acid :

2Al+6HBr2AlBr3+3H2.

This represents the mole ratio in which the reactants combine and in which the products are formed.

Since 2 moles Al requires 6 moles HBr, it implies that, given 4.22 moles Al and 5.0 moles HBr, then HBr is in excess and Al is the limiting reagent.

Hence all 5.0molHBr will react with 5.03=1.667molAl to form 1.667molAlBr3 and 5.02=2.5molH2

Mar 26, 2016

2.5 mol dihydrogen gas are formed.

Explanation:

Al(s)+3HBr(aq)AlBr3(aq)+32H2(g)⏐ ⏐

Clearly, hydrobromic acid is in deficiency (complete rxn requires >12mol HBr). From the equation, 12 mol dihydrogen gas are evolved per mole of HBr. Since 5 mol HBr are used, half of this quantity of H2 evolve.