Physical and Chemical Changes
• Physical Change: no composition change
– Examples?
• Chemical Change: composition changes
– Examples?
• Chemical Reactions involve chemical changes
• Chemical Equations describe chemical changes
reactants  products

reactants 
 products
4Fe ( s)  3O2 ( g )  2Fe2O3 ( s)
(s)
(l )
(g)
(aq)
solid
liquid
gas
aqueous
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Types of Reactions
Combination Reactions
A
2
Mg
+
+
B
A
O
B
2
O
Mg
O
Decomposition Reactions
A
2
H
B
O
H
A
+ B
2 H H +
O
O
2
Types of Reactions
Displacement Reactions
• Single Displacement
A
+
B
C
A
+
C
B
• Double Displacement
A
B
+
C
D
A
C
+
B
D
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Chemical Equations
Express identities and quantities of substances
involved in chemical or physical change
1. Write reactants and products
2. Balance atoms (add coefficients)
3. Adjust coefficients (small-whole numbers)
4. Check balancing
5. Specify state of matter
The Mole
•
•
•
•
12 eggs = 1 dozen eggs
12 bagels = 1 dozen bagels
6.02 x 1023 hydrogen atoms = 1 mol H atoms
6.02 x 1023 water molecules = 1 mol H2O
1 mole is a unit that contains 6.02 x 1023
(Avogadro’s Number)
How many water molecules are in 3.5 moles of water?
6.02  10 23 H 2O molecules
3.5 moles H2O 
 2.107  10 24
1 mole H 2O
2.1 1024 H 2O molecules
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Moles of Elements in a Formula
How many moles of each element are in 1 mole of water?
1 mole H2O
1 mole H 2 O
1 mole O
= 1 mole O atoms
= 2 moles H atoms
1 mole H 2 O
2 moles H
How many moles of each element are in 1 mole of glucose?
1 mole C6H12O6
1 mole C 6 H12O 6
6 moles C
= 6 moles C atoms
= 12 moles H atoms
= 6 moles O atoms
1 mole C 6 H12O 6
12 moles H
1 mole C 6 H12O 6
6 moles O
Molar Mass
• Number of grams of 1 mole of a substance is
called its molar mass.
• Same number as atomic or molecular mass
Examples:
Carbon
Water
Atomic mass:
12 amu
Molecular mass:
18 amu
Molar mass:
12 g
Molar mass:
18 g
Why do we use the unit of moles in lab instead of
molecules or atoms?
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Calculations with Molar Mass
You measure out 10.0 g of water.
How many moles of water do you have?
1 mole H 2 O
10.0 g H2O 
18 g H 2 O
 0.55555  0.56 moles H2O
If a piece of metal displaces 2.2 mL water,
how many water molecules has it displaced?
(Assume the density of water is 1.0 g/mL.)
1 g H 2 O 1 mole H 2 O 6.02  10 23 molecules
2.2 mL H2O 


1 mL H 2 O 18 g H 2 O
1 mole H 2O
 7.35778 10
22
22
7
.
4

10
molecules H 2O

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Molar relationships
C3H8 (g) + 5 O2 (g)  3 CO2 (g) + 4 H2O (g)
1 mol C3H8 reacts with _______ mols O2
1 mol C3H8 produces _______ mols CO2
1 mol C3H8 produces _______ mols H2O
5 mol O2 produces _______ mols CO2
2 mol C3H8 produces _______ mols CO2
Mass Calculations for Reactions
1. Write balanced equation
2. Convert given mass to mols
3. Convert to mols of other substance using
stoichiometric equivalents
4. Convert amount of second substance to mass,
number of entities, etc.
Sample Problem
How much carbon dioxide (in grams) is
produced when 3.00 g of ethanol (C2H6O)
combusts in air?
How much oxygen is used up to combust 5.00 g
of ethanol?
C2H6O (l) +
O2 (g) 
CO2 (g) + H2O (l)
Limiting Reactants
Chemical Reactions Involving
a Limiting Reactant
hydrazine (N2H4) and dinitrogen tetraoxide are
liquids that ignite to form nitrogen gas and water
vapor
How many grams of nitrogen gas form when 100. g
of N2H4 and 200. g of dinitrogen tetraoxide are
mixed?
Chemical Reactions in Practice:
Theoretical, Actual, and Percent Yields
• Theoretical yield: what we should get
(according to calculations)
• Actual yield: what we actually get
– Why? Side reactions, error, etc.
• Percent yield:
actual yield
% yield 
100
theoretica l yield
Oxidation-Reduction Reactions
• Movement of electrons from one reactant to another
• 2 Mg (s) + O2 (g) --> 2 MgO (s)
– Charge on magnesium? Oxygen?
• LEO GER
• Reducing agent? Oxidizing agent?
• Your car has a 15 gallon gas tank. How many
pounds of carbon dioxide are released to the
atmosphere for ever tank of gas you use while
driving your car?
• The reaction taking place in your engine is:
– Gasoline + Oxygen
Carbon Dioxide + water
– Hint: Gasoline is mostly Octane (C8H18)
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