1. Limiting Reactants/Reagents

2. What Is a Limiting Reactant?
Many cooks follow a recipe when making a new dish.
Let’s look at a recipe for the formation of a double cheeseburger:

3. 1 hamburger bun
1 tomato slice
2 slices of cheese
2 burger patties

4. If you want to make 5 double cheese burgers:
How many hamburger buns do you need? 5
How many hamburger patties do you need? 10
How many slices of cheese do you need? 10
How many slices of tomato do you need? 5

5. How many double cheeseburgers can you make if you start with:1
1 bun, 2 patties, 2 slices of cheese, 1 tomato slice 2
2 buns, 4 patties, 4 slices of cheese, 2 tomato slices
1 mole of buns, 2 moles of patties, 2 moles of cheese, 1 mole of tomato slices
1 mole
10 buns, 20 patties, 2 slices of cheese, 10 tomato slices 1

6. In chemical reactions….
Limiting Reactant—the reactant that restricts the amount of product that can form in a chemical reaction Reactant in Excess—the substance not fully used in a chemical reaction; some remains leftover

7. To determine the limiting reactant
If necessary, convert both reactants to moles from grams.
Use their mole to mole ratios to convert each reactant to moles of the other.
Compare the amount given to the amount needed to determine which would be limiting.
Use limiting reactant for all calculations.

8. Sample Problem
Silicon dioxide (quartz) readily reacts with hydrogen fluoride according to the following equation: SiO2 + 4HF  SiF4 + 2H2O If 6.0 mol HF is added to 4.5 mol SiO2, which is the limiting reactant?

9. Word equation: potassium + fluorine  potassium fluoride
Example: If 17.1g of potassium reacts with 14.3g of fluorine, which reactant is the limiting reactant and what mass of potassium fluoride can theoretically be produced?
Word equation: potassium + fluorine  potassium fluoride
Formula Equation: 2K + F2  2KF
17.1gK
14.3gF2
?gKF
17.1g K 1
1 mol K
39.10g K
2 mol KF
2 mol K x x =
0.437 mol KF
Potassium is the L.R.
14.3gF2 1
1 mol F2
38.00gF2
2 mol KF
1 mol F2 x x =
0.753 mol KF
0.437 mol KF x g KF = 25.4 g KF
1 mol KF

10. Limiting Reagent worksheet #1
Balance the equation
Convert grams to moles
Use moles of limiting reactant (mole-mole ratio)
Grams (limiting) moles(limiting)  mole product  grams product
Determine # moles used and moles in excess, convert moles in excess to grams in excess, subtract