1. Limiting Reactants
Section 12.3

2. Limiting Reactants
Rarely are the reactants in a chemical equation present in the exact ratios specified by the balanced equation. Generally, there is too much of one and not enough of the other. The chemical reaction will stop once one of the reactants is used up. This leaves the remainder of the reactant that was in excess unreacted. The chemical that you ran out of was the limiting reactant.

3. Limiting Factor Notesheet
Consider the following recipe:
3 cups flour + 2 eggs + 1 cup sugar + 2 tsp baking powder  12 muffins
A quick check of the pantry shows that the following quantities are available. How many muffins could be made with respect to each ingredient?
9 cups of flour could make ___36___ muffins
4 eggs could make __24__ muffins
8 cups of sugar could make __96___ muffins
10 tsp baking powder could make __60___ muffins

4. Limiting Factor Note sheet
3 cups flour + 2 eggs + 1 cup sugar + 2 tsp baking powder  12 muffins
What is the maximum number of muffins that could be made considering ALL ingredients? __24___
Which ingredient would you run out of first? _eggs____
This ingredient would be referred to as the __limiting_ __reactant____.
The other ingredients are said to be __in __ excess .
When you run out of an ingredient, you stop producing the _product__.

5. Limiting Factor Note sheet cont’d…
Consider the following “recipe” (equation):
2 mol of Al mol of Cl2  2 mol of AlCl3
A quick check of the chemistry lab shows that the following quantities are available. How much product could be made from each? (How many times could you make the recipe?)
10 moles Al ______
12 moles Cl2 _____

6. What is the maximum amount of AlCl3 that could be made considering all the ingredients? ________
We would say the aluminum is _________________ and the chlorine is _________________.
What if you were presented with grams of each reactant? Let’s say there are 100 g of Al and 125 g of Cl2 available. How much product could be formed? (Remember, the coefficients in the equation are mole numbers)
100 g of Al would yield ________ mol of product.
125 g of Cl2 would yield ________ mol of product.
How much product could be made considering both reactants? ________
The limiting factor would be ________.

7. Calculating the Product when the Reactant is Limited
In the following equation:
If 200 g of sulfur reacts with 100 g of chlorine what mass of sulfur chloride will be produced? x
S Cl2  4S2Cl2
Sulfur Chlorine
200 g = x g g = x g
256 g g g g
256x = x = 53600
x = g x = g  lowest #

8. Steps for Calculating Limiting Reactants
Balance the equation
Find the mass of each of the compounds (molar mass x’s coefficient)
Set up ratios for each of the reactants and solve
Look for the lowest number – this is your limiting reactant

9. Limiting Reactant Practice I
Balance the following formula:
N H2  NH3
1. If you had 112 grams of nitrogen, what is the maximum number of grams of NH3 that could be produced?
2. If you had 18 grams of hydrogen, what is the maximum number of grams of NH3 that could be produced?
3. What is the maximum number of grams of NH3 that can be produced with 112 grams of nitrogen and 18 grams of hydrogen?
5. What is the limiting reactant?

10. total needed already used additional needed
To Determine How Much More of the Limiting Reactant is Needed to Use Up the Excess Reactant and Finish the Reaction:
S Cl  S2Cl2
200 g = __x__
256 g g
256x = 56000
x = g g = g
total needed already used additional needed
to complete reaction x