Limiting Reactants

Obviously in chemical reactions not all the chemicals will be fully used up, usually there is one chemical that will be used up first, stopping the reaction. The chemical that will be used up first is called the Limiting
Reactant (LR).

Of course one needs to know how to find the limiting reactant before they can do much, which is what I will show you next.

For example
Find the LR when 2.2 moles of Sodium reacts with .19 moles of Oxygen.
First write the balanced chemical equation  4Na + O₂ -> 2Na₂O
Next you will take one of the chemicals and figure out how many moles of the second equation you need to fully react with the first equation I will use Sodium to start  2.2/1 x 1/4 = .55 mol (don't forget your significant digits)
Now how to interpret the answer the .55 means that you need .55 mol of Oxygen to fully react with the 2.2 mol of Sodium, of course you only have .19 mol of Oxygen, therefore Oxygen is the limiting reactant.

This method can also be expanded with using grams or liters etc. instead of moles but the basic equation is still the same.
If you're still not sure here's another example.
You have 1.40 L of  Calcium find the LR when calcium reacts with 2.00 mol of Nitrogen find the LR.
4Ca + 3N₂ ->  2Ca₂N₃ 
1.4/1 x 1/22.4 x 3/4 = .0469 mol
Therefore Calcium is the LR

And here's a question for you to solve, if you have 2 mol of Calvin and the monster under his bed can only eat 22 L will Calvin survive the night?