Stoichiometry.
Chapter 9, 10, & 11
Standard 3
Ms. Siddall
vocabulary
1.
2.
3.
4.
5.
6.
7.
8.
9.
Compound
Chemical formula
Coefficient
Stoichiometry
Mole
Molar mass
Molar volume
Avogadro’s number
Standard temperature and pressure
Anatomy of a chemical formula
chemical formula: a combination of symbols and
numbers that describe the amount and type of atoms
that form a compound.
Example:
CuSO4(aq)
Atomic symbols describe the type of atoms in the
compound
(copper, sulfur, oxygen)
subscript numbers describe the number of atoms in
the compound
(1 copper, 1 sulfur, 4 oxygen)
physical state of the compound is described using
subscript letters
(aq = aqueous)
study question 1
Na2O(s)
In the above formula:
1. How many sodium atoms?
2. How many oxygen atoms?
3. What is the physical state?
4. Is the compound ionic or covalent?
Standard 3a: describing chemical reactions
An equation describes a chemical reaction or
a physical change
 Reactants: chemicals that react
 Products: chemicals that are formed
 e.x. sodium + oxygen  sodium oxide
Na(s) + O2(g)  Na2O(s)
reactants
product
study question 2
Pb(NO3)3(aq) + KI(aq)  KNO3(aq) + PbI3(s)
1.
2.
3.
Label the reactants and the products in the
reaction above
Are the reactants and products covalent or ionic?
How many oxygen atoms are in the compound
Pb(NO3)3?
Symbols describing chemical
reactions
Copy table 11.1 (page 323)
That’s right – open your book to page
323 and copy that table into your notes…
go on… do it! This spot had better not
be blank when I check your notebook!
study question 3
1.
What do the following symbols mean?



2.
(l)
(aq)

Pb(NO3)3(aq) + KI(aq)  KNO3(aq) + PbI3(s)

Which compound is solid?
Balancing chemical equations
The Law of Conservation of Matter: Matter
cannot be created or destroyed.

For chemical equations: The total number of
each type of atom must be the same before
and after the reaction
Law:
Thou shall not create
or destroy matter
example

Sodium reacts with oxygen to produce
sodium oxide
Na(s) + O2(g)  Na2O(s)



How many sodium atoms react? 1
How many sodium atoms are in the
product? 2
This violates the law of conservation of
matter!
study question 4
NaI(s) + Cl2(g)  NaCl(s) + I2(s)
Count the number of
Count the number of
atoms on the reactants atoms on the products
side
side
Sodium ____
Sodium ____
Iodine ____
Iodine ____
Chlorine ____
Chlorine ____
Does this equation obey the law of
conservation of matter?
Example:
4 Na(s) + O2(g)  2 Na2O(s)
SUBSCRIPTS CAN NOT CHANGE!

Coefficients are used to balance the equation

number of atoms or formulas needed in
the reaction. These apply to the entire
formula (all the atoms)
4Na = 4 sodium atoms

2Na2O = 4 sodium atoms and 2 oxygen atoms

study question 5
2Cu(s) + O2(g)  2CuO(s)
Count the number of
Count the number of
atoms on the reactants atoms on the products
side
side
copper ____
copper ____
Oxygen ____
Oxygen ____
Does this equation obey the law of
conservation of matter?
Rules of Balancing Equations
1.
2.
Write the equation using
correct formulas. You may
NOT change the formula in any
way.
Balance the equation using
coefficients
Balancing example:
sodium and oxygen react to form sodium oxide
Na + O2  Na2O
Take atomic inventory: (you must obey the Law
of Conservation of Matter)
Reactants:
Na
O
1
2
Products:
Na
O
2
1
Problem: begin with 2 oxygen atoms but end with only 1
This breaks the law of conservation of matter.
Na + O2  2Na2O
(= Na2O + Na2O)
solution: Add the coefficient ‘2’ in front of Na2O
Take atomic inventory again:
Reactants:
Na
O
1
2
Products:
Na
O
4
2
Problem: begin with 1 sodium atom but end with 4.
This breaks the law of conservation of matter.
4 Na + O2  2Na2O
solution: Add the coefficient ‘4’ in front of Na
Take atomic inventory again:
Reactants:
Na
O
4
2
Products:
Na
O
4
2
4 sodium atoms combine with 1 oxygen molecule to
form 2 formula units of sodium oxide. This equation
obeys the Law of Conservation of Matter.
study question 6

BALANCE THE FOLLOWING REACTION:
H2(g) + O2(g)  H2O(l)
Balancing with polyatomic ions

Sometimes polyatomic ions break apart in a
chemical reaction and sometimes they do not
 e.x. sulfate appears on both sides of the
reaction so SO4 can be treated like one atom:
Mg(s) + CuSO4(aq)  MgSO4(aq) + Cu(s)
 e.x. carbonate breaks apart so atoms must
be balanced individually:
CaCO3(aq) + HCl(aq)  CaCl2(aq) + H2O(l) + CO2(g)
study question 7

Balance the following equations:
1.
Na2CO3(s) + HCl(aq)  NaCl(aq) + CO2(g) + H2O(l)
2.
K2SO4(aq) + CaCl2(aq)  CaSO4(s) + KCl(l)
Types of Chemical Reactions.
1. Combination.


Also called synthesis
Two or more reactants combine to
form one product
 e.x. 2 Na(s) + Cl2(g)  2 NaCl(s)
 A + B  AB
study question 8
Which equation represents a synthesis
reaction?

2Ca(s) + O2(g)  2CaO(s)

2KClO3(s)  2KCl(s) + O2(g)
2. Decomposition.

One reactant decomposes to form
two or more products.
 2H2O(l)  2H2(g) + O2(g)
 AB  A + B
study question 9
Which equation represents a decomposition
reaction?

Ca(s) + O2(g)  CaO(s)

2KClO3(s)  2KCl(s) + O2(g)
3. Single Replacement.

An atom replaces an ion in a compound.

Mg(s) + CuSO4(aq)  MgSO4(aq) + Cu(s)

Cl2(g) + 2KI(aq)  I2(s) + 2KCl(aq)

A + BC  AC + B
study question 10
Which equation represents a single replacement
reaction?
• 2NaI(s) + Cl2(g)  2NaCl(s) + I2(s)
• 2NaI(aq) + Pb(NO3)2(aq)  2NaNO3(aq) + PbI2(s)
4. Double Replacement.


Ions from different compounds switch
places.
CaCO3(s) + 2HCl(aq)  CaCl2(s) + H2CO3(aq)

AB + CD  AD + CB
study question 11
Which equation represents a double replacement
reaction?
• 2NaI(s) + Cl2(g)  2NaCl(s) + I2(s)
• 2NaI(aq) + Pb(NO3)2(aq)  2NaNO3(aq) + PbI2(s)
5. Combustion reactions.




A compound reacts with oxygen
often produces CO2 & H2O
e.x. C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
Note: a combustion reaction can also be a
decomposition or a combination reaction
study question 12

Write the balanced equation for the
reaction of CO with O2 to form CO2 and
identify the type of reaction.
Standard 3e:
The Arithmetic of Equations.

A balanced equation shows the
amount of each reactant and product
needed or produced in any reaction.
Example.


Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
One atom of magnesium combines with 2
formula units of HCl to form one formula
unit of magnesium chloride and one
molecule of hydrogen gas.

Use equation coefficients to solve quantitative
problems.
study question 13
4Na(s) + O2(g)  2Na2O(s)
1.
2.
3.
How many molecules of oxygen are
needed to react with 4 atoms of sodium?
How many oxygen atoms is that?
How many formula units of sodium oxide
are produced when 4 atoms of sodium
are used?
Example.



Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
If 1 atom of magnesium is used, 2 formula
units of HCl are needed to react.
If 6 atoms of magnesium are used, how
many formula units of HCl are needed?
6 atom Mg
2 Fo.U. HCl
1 atom Mg
= 12 Fo.U. HCl
Anatomy of a conversion
T-Chart:
multiply everything on top and
divide by everything on the bottom
Given(units) Units for answer
Units of given
What you
know
Conversion
factor
= answer
What
you
get
study question 14
Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)

if 4 molecules of H2 are created
1.
2.
how many Fo.U. of HCl are needed?
How many atoms of Mg are used?
Standard 3b: The Mole
Atoms and molecules are so small
scientists must use a large number of
atoms, molecules or formula units in order
to observe chemical reactions. This large
number is called: A Mole
Standard 3c: Avogadro’s Number
The number of particles in one mole =
Avogadro’s number
= 6.02 x 1023
= 602,000,000,000,000,000,000,000
Particles = atoms,
molecules,
formula units,
donuts…
study question 15

How many dollars would you have if you
had Avogadro’s number of dollars?


Avogadro’s number is convenient
because a mole of any chemical is easily
measured in the laboratory.
Instead of using 6.02 x 1023 atoms we
use 1 mole of atoms.
study question 16
4Na(s) + O2(g)  2Na2O(s)
1.
2.
3.
How many moles of O2 are needed to
react with 4 moles of sodium?
How many moles of O2 are needed to
react with 2 moles of sodium?
How many moles of Na2O are produced
when 2 moles of sodium are used?
particles
Moles
Standard 3e:
stoichiometry
coefficients
volume
Moles
1 mole
Molar mass(g)
Molar mass(g)
1 mole
mass

1 Mole of any atom has a
mass (in grams) numerically
equivalent to the mass of a
single atom (in amu). This
mass is displayed on the
periodic table.
study question 17

What is the mass of one mole of:


Aluminum?
Carbon?
Standard 3d: Molar Mass
= the mass of one mole of any substance.

Example: Na2O
Sodium = 23g/mole
Oxygen = 16g/mole
1 mole Na2O:
(2x23g/mole) + 16g/mole =
The molar mass for Na2O = 62g/mole
study question 18

calculate the molar mass of AlCl3 (don’t
forget units!)
examples

What is the mass of 3 moles of sodium
hydroxide?
Molar mass!
3 moles NaOH
40 g NaOH
1 mole NaOH

= 120 g NaOH
How many moles of carbon dioxide are in
a sample weighing 88g?
88g CO2
1 mole CO2
44g CO2
= 2 moles CO2
study question 19
A person produces just less than 0.5 moles
CH4 per day. How many grams is that?
The volume of a Mole
1 mole of any GAS has a
volume of 22.4L at standard
temperature and pressure
 Standard temperature = 0°C
 Standard pressure = 1atm
study question 20
1. What is the volume of 2 moles of gas?
2. What is the volume of 0.5 moles of gas?
(At standard temperature and pressure)
examples

What is the volume of 3 moles of helium?
3 moles He
22.4 L He
1 mole He

= 67.2 L He
How many moles of nitrogen are inside a
224L container?
224 L
1 mole N2
22.4 L
= 10 mole N2
study question 21
A person produces just less than 11.2L CH4
per day. How many moles is that
(assume STP conditions)?
Example.


Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
If 73g hydrochloric acid are used, how
many liters of hydrogen gas are produced?
73 g HCl 1 mole HCl
36.5 g HCl
1 mole H2
22.4L H2
2 moles HCl 1 mole H2
= 22.4 L H2
study question 22
3H2(g) + N2(g)  2NH3(g)


If one mole of nitrogen is used how
many moles of hydrogen are needed?
How many liters of hydrogen are needed
to produce 17g of NH3(g)?
examples

How many molecules are contained in 2
moles of CO2?
2 moles CO2
6 x 1023 molecules
= 12 x 1023 molecules
CO2
1 mole CO2
24
= 1.2 x 10

How many atoms are contained in 2
moles of CO2?
2 mol CO2 6 x 1023 molcs 3 atoms
1 mol CO2
1 molc CO2
= 36 x 1023 atoms
= 3.6 x 1024
study question 23
A cow produces about 1500L CH4 per day.
How many molecules is that?