The reactant that is completely used up first. It limits how much product can be made.
The reactant left over after the other has been used up.
The Sandwich Analogy
2 slices of bread + 1 filling → 1 sandwich.
If you have 10 slices but only 3 fillings → Filling is limiting. You can only make 3 sandwiches.
Percentage Yield
\( \% \text{ Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100 \)
Theoretical Yield is the maximum you could make. Actual Yield is what you actually get (always less, due to losses).
Limiting Reactant Calculation
Problem: 5.00 g of Mg reacts with 10.0 g of HCl. Find the limiting reactant.
\(
Mg + 2HCl \rightarrow MgCl_2 + H_2 \)
1. Moles of each:
\( n(Mg) = \frac{5.00}{24.31} = 0.206 \text{ mol} \)
\( n(HCl) = \frac{10.0}{36.46} = 0.274 \text{ mol} \)
2. Divide by coefficient:
\( Mg: \frac{0.206}{1} = 0.206 \)
\( HCl: \frac{0.274}{2} = 0.137 \)
3. Smallest Value → Limiting:
HCl is limiting.