Stoichiometry Equations 3
Now that we know a little about the basics of stoichiometry, it is time to consider it in
terms of a complete chemical equations.
Task1 – Cookie Lab
Chemical reactions provide two important pieces of information.
1. They tell us the type and number of atoms and molecules that interact and how
they arrange.
2. They tell us the relative number of moles of atoms and molecules that interact and
form.
Let us examine a chemical reaction to show how this is true.
Reaction ----->
1 H2
+
1 Cl2
2 HCl
1 molecule
of Cl2
2 molecules of
HCl
The reaction indicates that if we had 1 molecule of
H2, then
1 molecule
+
of H2
These are relative ratios therefore, if we had 10
molecules
10
molecules
If we had 1,000 molecules,
1,000
molecules
+
1,000
molecules
1 mole
+
1 mole
If we had a mole of Hydrogen then
+ 10 molecules
20 molecules
2,000
molecules
2 mole
Moles can be converted to masses, volumes or particles, therefore we can use a chemical
reaction to calculate how much of a substance will form or react. Stoichiometry is the
name we give to the process of using a chemical reaction to predict the amount of
products that might form or reactant that might be used up.
Task 2: Mole recipes
Balanced equations are like mole recipes. Consider part of a typical recipe for monster
Ingredients
Margarine
Sugar
Oatmeal
Eggs
# of cookies
Amounts Needed
1/2 cup
1 cup
4 cups
3
15 cookies
cookies.
Question
Answer
1. How much margarine is needed to make 30 cookies?
2. If you had 12 cups of oatmeal and enough other ingredients how many
cookies could you make?
3.. How many eggs are needed to make 60 cookies?
1 cups
45 cookies
12
Chemical reactions are like the recipe for the cookies. The balances in the equations
are mole recipes that tell us the # of moles that react and form.
The hamburger analogy:
My recipe for a bacon double cheeseburger is:




1 hamburger bun
2 hamburger patties
2 slices of cheese
4 strips of bacon
Based on this recipe:
1. If I have five bacon double cheeseburgers:
a. How many hamburger buns do I have?
b. How many hamburger patties do I have?
c. How many slices of cheese do I have?
d. How many strips of bacon do I have?
2. How many bacon double cheeseburgers can you make if you start with:
a. 1 bun, 2 patties, 2 slices of cheese, 4 strips of bacon
b. 2 bun, 4 patties, 4 slices of cheese, 8 strips of bacon
c. 1 dozen bun, 2 dozen patties, 2 dozen slices of cheese, 4 dozen strips of
bacon
d. 1 mole bun, 2 mole patties, 2 mole slices of cheese, 4 mole strips of bacon
e. 10 bun, 20 patties, 2 slices of cheese, 40 strips of bacon
3. If you had fixings for 100 bacon double cheeseburgers, but when you were
cooking you ruined 10 of them. What percentage of the bacon double
cheeseburgers do you actually make?
Now, the chemistry problem.
NOTE: The math and the concepts are identical to the above example. The only
difference is the recipe.
Here are two examples of chemical recipes:


Na+ + Cl- -> NaCl
1 mole of H2SO4 + 2 mole NaOH produce 1 mole Na2SO4 + 2 mole H2O
Based on the recipes above:
1. If I have 1 mole of NaCl
a. How many moles of sodium do I have?
b. How many moles of Chloride do I have?
2. If I want to make 5 moles of Na2SO4:
a. How many moles of H2SO4 do I need?
b. How many moles of NaOH do I need?
3. How much Na2SO4 can I make if I have:
a. 1 mole of H2SO4 and 2 mole of NaOH
b. 10 mole of H2SO4 and 20 mole of NaOH
c. 0.1 mole of H2SO4 and 0.2 mole of NaOH
d. 1 mole of H2SO4 and 20 mole of NaOH
e. 0.42 mole of H2SO4 and 0.65 mole of NaOH
f. 5 grams of H2SO4 and 5 grams of NaOH
Assignment #6 : Mole Recipes
For Example; In the following equation
Equation (balanced)
If we had 2 moles of C3H8 (g) then
_1_C3H8 (g) +
2 moles
_5_O2 (g)
10 moles
_3_CO2 (g) + _4_H2O (l)
6 moles
8 moles
Notice that all of the values in the table are in the same ratio as the balance in the
equation. C3H8 : O2 is always 1 : 5, CO2 : H2O is always 3: 4 . We call these ratios,
equation factors or mole ratio. The reactants and products in this equation always react
and form in these relative ratios.
Moles of ------>
C3H8 (g)
O2 (g)
CO2 (g)
H2O (l)
12 moles
2 moles
Complete the rest of this table using the
equation above
0.5 moles
5 moles
Task 3: Mole to Mole Stoichiometry
The following technique can be used to predict the # of moles that will react or form in an
equation.
1.
2.
3.
4.
Identify the given number of moles.
Identify the balance of the Given.
Identify the balance of the Desired (substance you wish to find ).
Multiply.
Balance of Desired
Moles of Given
X
(n)
Moles of Desired
(n)
=
Balance of Given
Using the balanced equation below , predict
1. The number of moles of C3H8 (g) that reacts to produce 8.4 moles of CO2 (g).
Equation (balanced)
_1_C3H8 (g) +
_5_O2 (g)
_3_CO2 (g) + _4_H2O (l)
Answer:
3 CO
8.4 moles of
C3H8 (g)
X
= 25.2 moles CO2 (g)
1 C3H8
2. The number of moles of H2O (l) that form if 63.7 moles of O2 reacts.
Answer:
4 H2O (l)
63.7 moles O2 (g)
X
=
51.0 moles H2O (l)
5 O2 (g)
Assignment #7: Mole to Mole Stoichiometry:
Answer the following questions using the mole ratio equation above.
1. In the cylinder of a car nitrogen reacts with oxygen according to the following unbalanced
equation.
___N2 (g)


+
___O2 (g)
___NO (g)
balance the equation.
calculate the number of moles of NO (g) that would form if 7.8 moles of N2
(g) reacted.
2. An orange precipitate of iron(III) hydroxide is formed when iron(III) chloride reacts with
sodium hydroxide. The unbalanced equation below describes the reaction.
__ NaOH(aq)
o
o
+
__ FeCl3(aq)
__Fe(OH)3 (s) +
__ NaCl (aq)
balance the equation.
Calculate the number of moles of Fe(OH)3 (s) that forms if 26.9 moles of
NaOH (aq) reacts.
3. A black solid of Lithium nitride forms when Lithium is (exposed to the air) and combines with
nitrogen. The unbalanced equation below describes this reaction.
___Li (s) + ___N2(g)


___Li3N (s)
balance the above reaction.
Calculate how many moles of Lithium nitride will form is 1.69 mol of
Lithium reacts.
4. Carbon in the form of charcoal in briquettes is unsafe to burn indoor due to the production of
carbon monoxide.


write a balanced chemical reaction for the burning of carbon in oxygen to
form carbon monoxide.
predict how many moles of carbon monoxide would be produced by the
burning of a 420 moles of carbon (charcoal briquettes ,approximately 5 Kg).
5. Butane when burned in a lighter undergoes a complete combustion. Write the chemical reaction
for the combustion , and calculate how much oxygen in moles is used when 0.19 moles of butane is
burned completely.
Task 4: Mole Method
We can use a simple 3 step method to solve stoichiometric questions with balanced
equations.
1. Identify the given and convert it to moles.
2. Identify the desired, and multiply the given number of moles by the mole
ratio or equation factor, to produce moles of desired substance..
3. Convert moles of desired substance to the units asked for in the question.
Example:
Question; What mass of methane gas in grams must burn to produce 365 grams of
water , by the following chemical reactions ?
_1_CH4(g) +
_2_O2(g)
_2_H2O (g)
+
_1_CO2(g)
1. Given is 365 g of water . Calculate moles of water. (mass(g)/ molar mass(g/mol).
365 g ÷18.02 g/mol
= 20.25 mole
2. Identify desired; mass of Methane gas . Multiple by mole ratio Balance CH4 ÷
Balance H2O
20.25 mol H2O (l)
X
1 CH4 (g)
=
10.13 mol CO2 (g)
2 H2O (g)
3. Convert moles of desired to the units asked for in the question. Mass of Methane
gas. ( multiply by molar mass of CO2(g) )
10.13 mol CO2
X
44.01 g/mol
= 446 g
Assignment # 8 : Mass to Mass Stoichiometry (Gravimetric )
1. Sulfur dioxide may be catalytically oxidized to sulfur trioxide. How many grams of
sulfur dioxide could be converted by this process if 100.0 grams of oxygen are available
for the oxidation by the following unbalanced chemical reaction?
___SO2 (g) +
___O2 (g)
___ SO3 (g)
2. Ferric oxide (Iron (III) oxide ) may be reduced to pure iron with coke ( pure carbon ) .
If we have 150 Kg of Iron (III) oxide how much coke would be needed to completely
convert it to iron by the following unbalanced equation.
___Fe2O3 (s)
+
___C (s)
___CO2 (g)
+
___Fe (s)
3. Calcium phosphate, silicon dioxide, and coke (C) may be heated together in an electric
furnace to produce phosphorus, as shown in the following unbalanced equation.
___Ca3(PO4)2
+ ___SiO2
+ ___C
___CaSiO3 +
___ CO
+
___P4
4. Sodium tetraborate is produced by combining boric acid with sodium hydroxide,
according to the following unbalanced chemical reaction.
___H3BO3
+
___NaOH
___H2O
+
___Na2B4O7
5. Gold will dissolve in the acid mixture known as aqua regia according to the following
reaction.
___Au + ___HNO3 +
___HCl
___AuCl3
+ ___NO +
___H2O
How much gold (III) chloride would be produced if 250 grams of HCl is consumed in the
reaction?
6. How many grams of ammonia will be evolved when 34 grams of ammonium chloride
is added to an excess of potassium hydroxide, by the following equation.
___NH4Cl
+ ___ KOH
___NH3
+
___H2O + ___KCl
Task 5: Gas stoichiometry
The same mole method is used to solve questions involving gas volumes. Converting to
and from moles requires us to multiply or divide by the molar volume (24.5 L/mol at
SATP )
Example:
Ammonia gas is reacted with sulfuric acid to form the important fertilizer ammonium
sulfate. What mass of ammonium sulfate can be produced from 85 kL of ammonia
reacting according to the reaction below at SATP (standard atmospheric temperature and
pressure )
_1_NH3
+
Answer:
Step 1: Convert given to moles.
_1_H2SO4
_1_(NH4)2SO4
85 kL
= 3.469 mol. NH3
24.5 L/mol
Step 2: Calculate the moles of desired, by multiplying by the mole ratio (balance of
Desired ÷ balance of Given )
3.469 mol. X _1_(NH4)2SO4
_1_NH3
= 3.469 mol. (NH4)2SO4
Step 3: Convert the moles of desired to the correct units, by multiplying by the molar
mass of ammonium sulfate.
3.469 mol.
X 114 g = 395 g
mol
Assignment #9 : Gas stoichiometry
1. Lightning discharges in the atmosphere catalyze the conversion of nitrogen gas to
nitric oxide gas. How many grams of nitrogen gas would be required to make 55 kL of
nitric oxide?
___N2 (g)
+
___O2 (g)
___N2O (g)
2. What mass of sulfur will be required to produce 150 L of sulfur dioxide when it is
burned in oxygen gas, according to the following unbalanced reaction.
___S8 (s)
+
___O2 (g)
___SO3 (g)
3. How much carbon monoxide in kL (at SATP ) will be produced when 150 grams of
calcium phosphate reacts with enough silicon dioxide and carbon, according to the
following unbalanced reaction.
___Ca3(PO4)2
+ ___SiO2 +
___C
___CaSiO3
+
___CO
+
___P4
4. Calcium phosphide when added to water produces phosphine gas (PH3). How many kL
at SATP of the gas will be produced when 350 grams of calcium phosphide is added to
an excess amount of water.
___Ca3P2
+
___H2O
___PH3
+
___CaO
Assignment 10: Stoichiometry Reactions
Stoichiometry Worksheet
Go to solutions
1. Silver sulfide (Ag2S) is the common tarnish on silver objects. What weight of
silver sulfide can be made from 1.23 g of hydrogen sulfide (H2S) obtained from a
rotten egg? The reaction of formation of silver sulfide is given below:
Ag(s) + H2S(g) + O2(g) Ag2S(s) + H2O(l) (Equation must first be balanced.)
2. A somewhat antiquated method for preparing chlorine gas involves heating
hydrochloric acid with pyrolusite (manganese dioxide), a common manganese
ore. (Reaction given below.) How many kg of HCl react with 5.69 kg of
manganese dioxide?
HCl(aq) + MnO2(s)  H2O(l) + MnCl2 (aq) + Cl2(g) (Equation must first be
balanced.)
3. Given the following equation: 2 KClO3 ---> 2 KCl + 3 O2
How many moles of O2 can be produced by letting 12.00 moles of KClO3 react?
4. Given the following equation: 2 K + Cl2 ---> 2 KCl
How many grams of KCl is produced from 2.50 g of K and excess Cl2. From 1.00
g of Cl2 and excess K?
5. Given the following equation: Na2O + H2O ---> 2 NaOH
How many grams of NaOH is produced from 1.20 x 102 grams of Na2O? How
many grams of Na2O are required to produce 1.60 x 102 grams of NaOH?
6. Given the following equation: 8 Fe + S8 ---> 8 FeS
What mass of iron is needed to react with 16.0 grams of sulfur? How many grams
of FeS are produced?
7. Given the following equation: 2 NaClO3 ---> 2 NaCl + 3 O2
12.00 moles of NaClO3 will produce how many grams of O2? How many grams
of NaCl are produced when 80.0 grams of O2 are produced?
8. Given the following equation: Cu + 2 AgNO3 ---> Cu(NO3)2 + 2 Ag
How many moles of Cu are needed to react with 3.50 moles of AgNO3? If 89.5
grams of Ag were produced, how many grams of Cu reacted?
9. Molten iron and carbon monoxide are produced in a blast furnace by the reaction
of iron(III) oxide and coke (pure carbon). If 25.0 kilograms of pure Fe2O3 is used,
how many kilograms of iron can be produced? The reaction is: Fe2O3 + 3 C ---> 2
Fe + 3 CO
10. The average human requires 120.0 grams of glucose (C6H12O6) per day. How
many grams of CO2 (in the photosynthesis reaction) are required for this amount
of glucose? The photosynthetic reaction is:
6 CO2 + 6 H2O ---> C6H12O6 + 6 O2