Limiting reactants – notes and Stoich ws 3
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Honors Chemistry
 When two substances react one may run out first and the other will not be completely used up
 The limiting reactant is the substance that limits the reaction (runs out first)
Hamburger Example: A hamburger consists of one bun, one meat patty, three slices of pickle, two
slices of tomato, six grams of ketchup, and four grams of mustard. Write a balanced equation to
represent the composition on one hamburger.
1. You start making hamburgers and you have 3000 buns, 2900 meat patties, 8500 pickle slices, 7400 tomato slices,
20,000 grams of ketchup, and 18,000 grams of mustard. This information has been recorded in the table below.
2. Next, determine how many ‘whole’ hamburgers can be made from each ingredient (reactant).
3. Finally, identify which ingredient runs out first. (This is your Limiting Reactant = LR). Circle the quantity of
“whole” hamburgers that can be made. When the LR runs out, you can’t make any more hamburgers.
4. Calculate how much extra of each ingredient is left over. (Excess)
Ingredient
(Reactant)
Start
Quantity
Bun
3000 buns
Patty
2900 patties
Pickle
8500 pickles
Tomato
7400 tomato slices
Ketchup
20,000 grams ketchup
Mustard
18,000 grams mustard
Quantity per
Hamburger
Possible Whole
Hamburgers
Amount of extra
(Excess Reactant)
Steps for solving stoichiometry problems involving limiting reactants
1. Check/Write the balanced equation for the reaction
2. Convert known masses of reactants into moles
3. Using the numbers of moles of the reactants and the appropriate mole rations, determine which reactant is
limiting (note to determine the limiting reactant you are only looking at the reactants)
ex: A + B -> product(s)
If the calculated amount for B is greater than the actual amount of B, then B it is the limiting reactant
If the calculated amount for B is less than the actual amount of B, then A is the limiting reactant
4. Using the amount of the limiting reactant and the appropriate mole ratios compute the number of moles of
the desired product
5. Convert from moles of product to grams of product using molar mass, if required by the problem
There are two basic types of limiting reactant questions
I. Short simple type (reactant to reactant) - What is the limiting reactant? (Only look at the reactants – steps 1-3)
II. Longer, multi-question, multi-step type - How much product will be formed or how much reactant will be used or
how much excess reactant is left when producing a certain amount of product? (These questions require that we
first find the limiting --steps 1-5)
I.
What is the limiting reactant?
1a. If 42 grams of hydrogen fluoride reacts with 39 grams of SiO2, which is the limiting reactant?
SiO2 +4HF -> SiF4 + 2 H2O
II.
How much reactant is used or excess reactant available or product is formed?
Continue with the above problem and complete 1b-1d.
1b. How much SiO2 will be used?
1c. How many grams of SiO2 are excess?
1d. How many moles and how many grams of SiF4 will be produced? Note, you must start your equation with the
information given for the limiting reactant.
2. Refer to the equation N2H4 + 2H2O2 -> N2 + 4 H2O
2a. What is the limiting reactant when 2.350 g N2H4 is mixed with 1.750 grams of H2O2.
2b. How much N2 is produced in moles and grams ?
3. Consider the reaction: 3 NH4NO3 + Na3PO4  (NH4)3PO4 + 3 NaNO3
Assuming we started with 30.00 grams of ammonium nitrate and 50.00 grams of sodium phosphate.
3a. Which of the reactants is the limiting reactant? (First, convert 30.00 grams of ammonium nitrate to grams of
sodium phosphate.)
The limiting reactant is ____________________
3b. What is the maximum amount of each product that can be formed? (Note, you must start with the given grams of
the limiting reactant. Then find the grams of each product that can be produced.)
3c. How much of the other reactant is left over after the reaction is complete? (Note, calculate how many grams of
excess were not consumed.)
4. Consider the reaction: 3 CaCO3 + 2 FePO4  Ca3(PO4)2 + Fe2(CO3)3
Assuming we start with 100 grams of calcium carbonate and 45 grams of iron (III) phosphate.
4a. Which of the reactants is the limiting reagent?
4b. What is the maximum amount of each product that can be formed?
4c. How much of the other reactant is left over after the reaction is complete?
5. Consider the reaction of acetic acid, C2H3O2H with aluminum hydroxide to form water and aluminum acetate,
Al(C2H3O2)3:
5a. Write the balanced equation
Determine the mass of aluminum acetate that can be made if I do this reaction with 125 grams of acetic acid and 275
grams of aluminum hydroxide. (Note, you must first find the limiting reactant.)
5b. What is the limiting reactant?
5c. What is mass of aluminum acetate that can be made?
5d. How much of the excess reactant will be left over after the reaction is complete?
6. Consider the reaction: copper (II) chloride reacts with sodium nitrate, copper (II) nitrate and sodium chloride are
formed.
6a. Write the balanced equation for the reaction given above:
If 15.00 grams of copper (II) chloride react with 20.00 grams of sodium nitrate
6b. What is the limiting reactant?
6c. how much sodium chloride can be formed?
6d. How much of the nonlimiting reagent is left over in this reaction?