Question

According to this reaction: `2Al+6HBr -> 2AlBr_3 + 3H_2` If 4 moles of `Al` react with 8 moles of `HBr`, how many moles of `H_2` are formed?

Answer 1

`6` `"moles"` of `H_2(g)` are formed.

Explanation:

`2Al(s) + 6HBr(aq) rarr 2AlBr_3(aq) + 3H_2(g)uarr`

You have the chemical equation, it tells you EXPLICITLY, that 2 moles of aluminum metal give 3 moles of dihydrogen gas upon reaction. You started with 4 moles of aluminum, thus `3/2` that quantity of dihydrogen are formed.

This problem was posed to introduce you to stoichiometry, which is a fancy way of saying garbage in equals garbage out. We practise stoichiometry on a smaller scale when we balance our bank accounts, or even when we make a cash or electronic transaction. The debit made to out account for goods of a certain value, must equal the credit made to the account of the vendor who sold you the goods. Likewise, when you hand a shopkeeper a £10-00 note to cover a purchase, the value of the goods purchased + the change you receive must equal £10-00.