I don’t understand this question

Question

Use the equation 2 Al + 3 Cl2 —> 2 AlCl3. If 2 moles of aluminum and 2 moles of chlorine are reacted, identify the limiting reactant

Answer 1

Hi, Melanie,

The balanced equation 2 Al + 3 Cl2 —> 2 AlCl3 tells us that it takes 3 moles of Cl₂ to completely react with 2 moles of Al. If they aren't in the ratio of 3 moles Cl₂ to 2 moles Al, there will be a surplus of one relative to the other. The one in shortest supply is termed the "limiting reagent." It means that there is not enough of it to completely consume the other reactant(s).

If 2 moles of aluminum and 2 moles of chlorine are reacted, we can use the molar ratio of (2 moles Al/3 moles Cl₂) to tell us how much Al we would need for the 2 moles Cl₂:

(2 moles Al/3 moles Cl₂)*(2 moles Cl₂) = 4/3 moles Al. We have two moles, so there is plenty. The Cl₂ must be the limiting reagent.

We can also write the factor as (3 moles Cl₂/2 moles Al), and use it to determine how much chlorine will be needed:

(3 moles Cl₂/2 moles Al)*(2 moles Al) = 3 moles Cl₂

We only have 2 moles Cl₂, so it is the limiting reagent.

I hope this helps,

Bob