Question

In the reaction `2Al +6HBr -> 2AlBr_3 + 3H_2`, when 3.22 moles of `Al` reacts with 4.96 moles of `HBr`, how many moles of `H_2` are formed?

Answer 1

`2.48mol`

Explanation:

The balanced chemical equation represents the mole ratio in which the chemicals react.

Since 2 moles aluminuim are required for every 6 moles of hydrogen bromide, yet we only have 3.22 moles aluminium and 4.96 moles hydrogen bromide, it implies that `HBr` will get used up first and is hence the limiting reactant, while `Al` is in excess.

So all `4.96 mol HBr` is used up and reacts with `4.96/3=1.653mol Al` to produce `4.96/2=2.48 mol H_2`.