Chemistry- Stoich?

Question

Aluminum reacts with oxygen to produce aluminum oxide. If you want to produce 5.00 moles of aluminum oxide, how many moles of aluminum and how many moles of oxygen will be required?

Answer 1

4Al + 3O2 -----> 2Al2O3

4 moles of Al provides 2 moles Al2O3, so 4 x 2.5 moles Al will provide 5 moles Al2O3.

This will require 3 x 2.5 moles O2.

Answer 2

First, you want to write out the reaction:

4Al(s) + 3O2(g) -----> 2Al2O3(s)

Secondly, use the stoichiometric coefficents to solve the problem. This is how I would set it up.

To find the moles of Al:

5.00mol Al2O3 x (4mol Al / 2mol Al2O3) = 10.0mol Al

To find the moles of O2:

5.00mol Al2O3 x (3mol O2 / 2mol Al2O3) = 7.50mol O2

Essentially, you are using the stoichiometric relationships obtained from the equation to solve the problem. The equation tells you that if you have 4mol Al and 3 mol O2 you will get 2mol of Al2O3. In this case, you have 5mol of Al2O3, so you need to use the calculations above to solve.