Limiting Reactants Flashcards

All 5 cards in this deck

What is the limiting reactant?

The reactant that is completely used up, which limits the amount of product formed.

What does it mean to say a reactant is in excess?

There is more of it than is needed to react with all of the other reactant, so some is left over.

What are the steps to identify the limiting reactant?
e.g. 0.2 mol Mg with 0.05 mol $\mathrm{O_2}$ in $2\mathrm{Mg} + \mathrm{O_2} \rightarrow 2\mathrm{MgO}$

1. Find the moles of each reactant: 0.2 mol Mg, 0.05 mol $\mathrm{O_2}$
2. Divide each by its balancing number: $0.2/2 = 0.1$ and $0.05/1 = 0.05$
3. The smallest value is the limiting reactant: $\mathrm{O_2}$

Which reactant's amount do you use to calculate the maximum mass of product?

The limiting reactant, because it is used up first and limits the amount of product.

True or false? The reactant with the smaller mass is always the limiting reactant.

False. You must compare the amounts in moles against the ratio in the balanced equation.