Name:____________________________________________ Date: _______ Per. ______
Limiting Reactants
What determines the amount of product made in a chemical reaction?
Why?
In any chemical reaction, the amount of product made is dependent upon the
amount of reactants available. Typically, one or more reactants are completely
used up or consumed in the reaction. This activity will demonstrate how
stoichiometric calculations can be used to determine which reactant will limit
the amount of product made in the reaction.
Model 1
S’more Recipe
 2 graham cracker pieces
 1 marshmallow
 4 chocolate squares
+
2G + M + 4Ch
+
G2MCh4
Ingredients Available
 10 graham cracker pieces
 6 marshmallows
 16 chocolate squares
1) According to Model 1, how much of each ingredient is needed to make a s’more?
Graham cracker
Marshmallow
Chocolate square
2) According to Model 1, how much of each ingredient do you have to make s’mores?
Graham cracker
Marshmallow
Chocolate square
3) How many s’mores could you make using the recipe in Model 1 and the ingredients
listed?
4) How much of each ingredient will you have left over after you have made the maximum
amount of s’mores using the ingredients given in Model 1?
Graham cracker
Marshmallow
Chocolate square
5) Which ingredient(s) did you have in excess and could use to make more s’mores?
6) Which ingredient was completely consumed when you made the s’mores?
7) Which ingredient(s) limited the amount of s’mores you could make?
8) a) You are given the following ingredients to make s’mores. Using the recipe above,
determine the number of s’mores you could make with these ingredients.
Graham cracker
24
Marshmallow
35
Chocolate square
60
b) How much of each ingredient would you have leftover?
Graham cracker
Marshmallow
Chocolate square
9) In question #8, what ingredient(s) would you have in excess? What ingredient(s) would
you use up completely when making s’mores?
10) Using what you have learned from model 1, write a definition for the term limiting
reactant. Write your answer using a complete sentence.
Read This!
The limiting reactant in a chemical reaction is the reactant that is completely consumed
in the reaction. No more product can be made because the limiting reactant has been
used up completely. Thus, the limiting reactant limits the amount of product made in
the reaction. The limiting reactant also is referred to as the limiting reagent.
Model 2
2H2 + O2 → 2 H2O
Reactants
2 molecules H2
1 molecule O2
2 moles H2
1 moles O2
4 g H2
32 g O2
Products
2 molecules H2O
2 moles H2O
36 g H2O
12) Using the information given in Model 2, how many hydrogen (H2) and oxygen (O2)
molecules would you need to produce 2 molecules of water (H2O)?
13) Using the information given in Model 2, how many moles of hydrogen and oxygen
molecules would you need to produce 2 moles of water?
14) Using the information given in Model 2, how many grams of hydrogen and oxygen
molecules would you need to produce 36 grams of water?
15) Suppose you have 10 molecules of hydrogen and 24 molecules of oxygen.
a) How many molecules of water could you produce?
b) What reactant would be the limiting reactant? Explain your reasoning.
16) You have 72 molecules of H2 and an unlimited supply of O2 molecules.
a) How many molecules of H2O can you make?
b) How many molecules of O2 would you use in the reaction?
17) Suppose you have 14 moles of H2 molecules and 14 moles of O2 molecules.
a) How many moles of H2O can you make?
b) What reactant would be the limiting reactant? Explain your reasoning.
18) You have 30 moles of oxygen gas molecules.
a) How many moles of hydrogen molecules would you need to react completely with
the oxygen molecules?
b) What is the maximum number of moles of water you could produce with 30 moles of
O2?
19) You have 16 grams of H2 and 64 grams of O2.
a) Identify the limiting reactant. Justify your answer with calculations or an explanation.
b) What is the maximum amount, in grams, of water that could be produced from 16
grams of H2 and 64 grams of O2.
20) Explain how you could identify the limiting reactant in a chemical reaction.
21) It is possible to use stoichiometry to calculate the amount of product produced in a
chemical reaction. When doing such a calculation, would it be better base your
calculation on the amount of limiting reactant or on the amount of excess reactant?
Justify your answer.