Stoichiometry
Stoichiometry Steps
1. Balance the equation;
Is it balanced?
Is it balanced?
Mole Box
Grams A
Grams B
Molar Mass
of A
Molar Mass
of B
Mol A
Mol B
Mole Ratio
(Balanced Equation)
2. Grams to Moles (Divide by Molar Mass)
*Don’t forget to use sig figs!*
A sample contains 27.1 g of oxygen. How many moles of oxygen are in this sample?
27.1 grams of O2 X 1 mole O2 =
32 grams O2
This is the molar mass
of Oxygen.
(16.00g X 2)= 32.00g
of O2
0.847 moles
of O2
*THIS IS A ONE STEP PROBLEM!*
3. Moles to Moles ( Multiply by Mole Ratio)
If
you started with 3.50 mol of hydrogen, how many
moles of oxygen could be formed?
3.50 mol H2 X 1 mole O2 = 1.75 moles of O2
2 moles H2
4. Mole to Grams (Multiply by Molar Mass)
If you needed to produce 12.2 g of water, how many
grams of hydrogen would you need?
12.2 moles of H2O X 2 moles H2 X 2 grams H2 = 24.4 grams of H2
2 moles H2O 1 mole H2
*THIS IS A TWO STEP PROBLEM!*
Molarity
The concentration of a solution in
= moles of solute
1 L of solution
mol/L
Finding Moles of a Solution
Use the formula;
cv = n
Concentration(mol/L) X Volume(L) = Moles(mol)
Mole Box 2
Grams B
Grams A
Molar Mass
of A
Molar Mass
of B
Mol B
Mol A
Mole Ratio
(Balanced Equation)
Concentration
of A (mol/L)
Litres A
Concentration
of B (mol/L)
Litres B
Example
(Litres A to Grams B)
2 NaOH(aq) + H2SO4(aq)
Na2SO4(aq) + 2H2O(l)
15.0 mL of a 1.5 mol/L NaOH solution gives how many
grams of H2O?
CONVERT!
1L = XL
1000 mL 15.0 mL
X= 0.0150 L
0.0150 L NaOH X 1.5 mol NaOH X 2 mol H2O X 18g H2O = 0.405 g
1 L NaOH 2 mol NaOH 1 mol H2O H2O
*THIS IS A THREE STEP PROBLEM!*
Stoichiometry with Gases
The stoichiometry of gases is based on
the ratio between the quantities of gas
involved in a chemical reaction. This
method is used to predict the quantity
of a reactant or product involved in a
chemical reaction in which one of the
compounds is a gas.
Example 1
(Litres A to Litres B)
If 7.00 L of H2 gas reacts with Cl2 gas,
how many litres of HCl gas would form?
H2 + Cl2
2HCl
7.00 L H2 X 2 L HCl = 14.0 L HCl
1 L H2
Example 2
(Grams A to Litres B)
Mg(s) + HCl(aq)
MgCl2(aq) + H2(g)
If 17.00 g of Mg reacts, how many
millilitres of H2 will form?
17.00 g Mg X 1 mol Mg X 1 mol H2 X 22.4 L H2 = 15.70 L of H2
24.31 g Mg 1 mol Mg 1 mol H2
1 L = 15.70 L X= 15 700 mL of H2
1000 mL X mL
Convert this
answer to
millilitres!
Classifying Reactions
1. Combustion= Burning with Oxygen
Tips:
 If C is in the reactants, CO2 will be a
product.
Example:
• C + O2
CO2
 If H2 is in the reactants, H2O will be a
product.
Example:
• 2H2 + O2
2H2O
• CH4 + 2O2
CO2 + 2H2O
2. Synthesis
Simpler reactants combine to make more
complex products.
Examples:
• Mg + Cl2
• CO2 + H2O
MgCl2
H2CO3
3. Decomposition
Decomposition is when complex Reactants
break down to become simpler molecules.
Examples:
• H2CO3
• BF3NH3
H2O + CO2
BF3 + NH3
4. Single Displacement
An element and a compound are required for
single displacement. The element in the
reactants will “replace” or “displace”
one of the elements in the compound.
*It is important to remember that metals
replace metals only, and non-metals replace
non-metals only.
Examples:
• A + B
B + AC
• Na(s) + H2O(l)
NaOH(aq) + H2(g)
Example of a Reaction
Burning of methane releases 275 kJ of
energy per mole of methane being
burned. How many grams of methane must
burn in order to produce 1500 kJ of
energy? What type of reaction has occurred? Combustion reaction.
CH4 + 2O2
CO2 + 2H2O
1500 kJ X 1 mole CH4 X 16.04 g CH4 = 88 g
275 kJ
1 mole CH4 of CH4
C = 12.01
H = 1.01
12.01 + 1.01(4) = 16.04 g of CH4
Bibliography
• Couture, Ivan, Marie-Eve Lacombe-Harvey, and
Genevieve Levasseur-Thériault. Quantum Chemistry
Student Textbook. Ed. Marie-Eve Robitaille, Isabel
Rusin, and Colleen Ovenden. Trans. Jacquie Charlton,
Cristina Cusano, Natasha DeCruz, Joann Egar, and
Gwen Schulman. Montreal: Cheneliere Education,
2011. Print.
• Doty, Wendy L. "Stoichiometry Notes." Downey
Unified School District. N.p., 2006. Web. 10 Oct. 2012.
<http://www.dusd.net/staff/rcramm/Chemistry/Unit_8/S
toichiometery%20Notes.pdf>.