# 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?

Apr 17, 2016

#### Answer:

$6$ $\text{moles}$ of ${H}_{2} \left(g\right)$ are formed.

#### Explanation:

$2 A l \left(s\right) + 6 H B r \left(a q\right) \rightarrow 2 A l B {r}_{3} \left(a q\right) + 3 {H}_{2} \left(g\right) \uparrow$

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 $\frac{3}{2}$ 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.