Limiting Reagents Flashcards

All 6 cards in this deck

What is the limiting reactant in a reaction?

The reactant that is completely used up first, and which is not in excess.

Why is the mass of product formed controlled by the limiting reactant?

Once it is used up the reaction stops, so no more product can be made however much of the other reactant is left.

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

More of it is present than is needed to react with all of the other reactant, so some is left over at the end.

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

False. It is the one that runs out first, found by comparing moles against the ratio in the balanced equation.

What are the steps to identify the limiting reactant?

e.g. 0.1 mol Mg and 0.1 mol HCl in $\mathrm{Mg} + 2\mathrm{HCl} \rightarrow \mathrm{MgCl_2} + \mathrm{H_2}$

1. Find the moles of each reactant: Mg $= 0.1$, HCl $= 0.1$
2. Compare with the equation ratio (1 Mg : 2 HCl): 0.1 mol Mg would need 0.2 mol HCl
3. The one that runs out first is limiting: HCl

Which reactant's moles must be used when calculating the maximum mass of product?

The moles of the limiting reactant.