1

•
Physical Changes are changes to matter that do not result in a change of the fundamental components that make that substance
– State Changes – boiling, melting, condensing
• Chemical Changes involve a change in the fundamental components of the substance
– Produce a new substance
–
Chemical reaction
–
Reactants

Products
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•
Density is a property of matter representing the mass per unit volume
•
For equal volumes, denser object has larger mass
•
For equal masses, denser object has small volume
•
Solids = g/cm 3
–
1 cm 3 = 1 mL
•
Liquids = g/mL
Density

Mass
Volume
•
Density : solids > liquids >>> gases
•
Water: density = 1g/ml Iron: density = 7.86 g/cm 3
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•
Freezes at 0°C
– At 1 atm, solid at 0°C or below
– Normal freezing point = normal melting point
• Boils at 100°C
–
At 1 atm, liquid up to 100°C, then turns to steam
–
Normal boiling point
– Boiling point increases as atmospheric pressure increases
• Temperature stays constant during a state change
•
Relatively large amounts of energy needed to melt solid or boil liquid
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•
As heat added to solid, it first raises the temperature of the solid to the melting point
•
Then added heat goes into melting the solid
– Temperature stays at the melting point
–
Heat of Fusion
• As more heat added it raises the temperature of the liquid to the boiling point
•
Then added heat goes into boiling the liquid
–
Temperature stays at the boiling point
–
Heat of Vaporization
•
As more heat added it raises the temperature of the gas
5

The heating/cooling curve for water heated or cooled at a constant rate
6

Both liquid water and gaseous water contain H
2
O molecules
7

Representations of the gas, liquid, and solid state
8

Intramolecular (bonding) forces exist between the atoms in a molecule and hold the molecule together
9

•
Solids can change directly into gases without going through the liquid state
•
Dry ice is solid CO
2
; it never melts under normal conditions. Instead it sublimes to gaseous CO
2
.
•
The formation of frost is reverse of sublimation = vapor deposition
10

not
•
When ionic compounds dissolve in water they dissociate into ions
– ions become surrounded by water molecules hydrated
•
When solute particles are surrounded by solvent molecules we say they are solvated
11

When solid sodium chloride dissolves, the ions are dispersed randomly throughout the solution
12

Polar water molecules interact with the positive and negative ions of a salt
13

• Covalent molecules that are small and have “polar” groups tend to be soluble in water
•
The ability to H-bond with water enhances solubility
H
C O
14

•
Larger attractive forces between molecules in pure substance means
– higher boiling point
– higher melting point (though also depends on crystal packing )
•
Like dissolves Like
–
Polar molecules dissolve in polar solvents
• Water, alcohol
• Molecules with O or N higher solubility in H
2
O due to Hbonding with H
2
O
– Non-polar molecules dissolve in non-polar solvents
• Oils and gasoline
15

•
Requires overcoming intermolecular attractions
•
Condensation is the reverse process
•
In a closed container, eventually the rate of evaporation and condensation are equal
– Equilibrium
–
In open system, evaporation continues until all liquid evaporated
16

Behavior of a liquid in a closed container. The system is at equilibrium.
17

• Pressure exerted by a vapor in equilibrium with a liquid
–
Or solid
•
Increases with temperature
• Larger intermolecular forces = Lower Vapor Pressure
• Liquid boils when its Vapor Pressure = Atmospheric Pressure
– Normal boiling point
–
Raising external pressure raises boiling point, & visa versa
Equilibrium
Liquid just poured into open container, little vapor
Evaporation faster than Condensation
Evaporation as fast as Condensation
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19

•
Reactions involve chemical changes in matter resulting in new substances
•
Reactions involve rearrangement and exchange of atoms to produce new molecules
–
Elements are not transmuted during a reaction

20

• a chemical change occurs when new substances are made
• visual clues (permanent)
– color change, precipitate formation, gas bubbles, flames, heat release, cooling, light
• other clues
– new odor, permanent new state
21

Bubbles of hydrogen and oxygen gas form when an electric current is used to decompose water
22

Hot and cold pack reactions
23

Chemical reactions
24

Chemical reactions
25

Chemical reactions
26

Chemical reactions
27

•
Shorthand way of describing a reaction
•
Provides information about the reaction
–
Formulas of reactants and products
–
States of reactants and products
–
Relative numbers of reactant and product molecules that are required
–
Can be used to determine weights of reactants used and of products that can be made
28

•
Matter cannot be created or destroyed
•
In a chemical reaction, all the atoms present at the beginning are still present at the end
•
Therefore the total mass cannot change
•
Therefore the total mass of the reactants will be the same as the total mass of the products
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•
Use proper formulas for each reactant and product
• proper equation should be balanced
– obey Law of Conservation of Mass
– all elements on reactants side also on product side
– equal numbers of atoms of each element on reactant side as on product side
• balanced equation shows the relationship between the relative numbers of molecules of reactants and products
– can be used to determine mass relationships
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1. Count atoms of each element
• polyatomic ions may be counted as one “element” if it does not change in the reaction
Al + FeSO
4

Al
2
(SO
4
)
3
+ Fe
1 SO
4
3
• if an element appears in more than one compound on the same side, count each separately and add
CO + O
2

CO
2
1 + 2 O 2
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2. Pick an element to balance
3. Find Least Common Multiple and factors needed to make both sides equal
4. Use factors as coefficients in equation
• if already a coefficient then multiply by new factor
5. Recount and Repeat until balanced
32

• when magnesium metal burns in air it produces a white, powdery compound magnesium oxide
– burning in air means reacting with O
2
1.
write the equation in words
– identify the state of each chemical magnesium + oxygen
 magnesium oxide
2.
write the equation in formulas
– identify diatomic elements
– identify polyatomic ions
– determine formulas
Mg + O
2

MgO
33

• when magnesium metal burns in air it produces a white, powdery compound magnesium oxide
– burning in air means reacting with O
2
3.
count the number of atoms of on each side
– count polyatomic groups as one “element” if on both sides
– split count of element if in more than one compound on one side
Mg + O
2

MgO
1

Mg

1
2

O

1
34

• when magnesium metal burns in air it produces a white, powdery compound magnesium oxide
– burning in air means reacting with O
2
4.
pick an element to balance
– avoid element in multiple compounds
5.
find least common multiple of both sides & multiply each side by factor so it equals LCM
Mg + O
2

MgO
1

Mg

1
1 x 2

O

1 x 2
35

• when magnesium metal burns in air it produces a white, powdery compound magnesium oxide
– burning in air means reacting with O
2
6.
use factors as coefficients in front of compound containing the element
 if coefficient already there, multiply them together
Mg + O
2

2 MgO
1

Mg

1
1 x 2

O

1 x 2
36

• when magnesium metal burns in air it produces a white, powdery compound magnesium oxide
– burning in air means reacting with O
2
7.
Recount
Mg + O
2

2 MgO
1

Mg

2
2

O

2
8.
Repeat
2 Mg + O
2

2 MgO
2 x 1

Mg

2
2

O

2
37

• methane gas burns to produce carbon dioxide gas and liquid water
– whenever something burns it combines with O
2
(g)
CH
4
+ O
2

CO
2
+ H
2
O
H
H
H
C
H
+
O
1 C + 4 H + 2 O
O
O
C
+
O
H H
O
1 C + 2 O + 2 H + O
1 C + 2 H + 3 O
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• to show the reaction obeys the Law of
Conservation of Mass it must be balanced
CH
4
+ 2 O
2

CO
2
+ 2 H
2
O
H
H
H
C
H
+
O O
O
+
O
1 C + 4 H + 4 O
O
C
O
+
O
H H
+
O
H H
1 C + 4 H + 4 O
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•
Incomplete combustion of carbon compounds occurs when there is not enough oxygen to fully make CO
2
.
2 C
4
H
10
+ 13 O
2
----> 8 CO
2
+ 10 H
2
O
2 C
4
H
10
+ 9 O
2
----> 8 CO + 10 H
2
O
•
CO is called a by-product (not the intended product)
40

•
CO concentrations can be reported in the parts per million scale (ppm)
– ppm tells how many particles out of a million are the compound in question
–
Air normally has 2 ppm CO
•
CO is a common pollutant from burning fossil fuels like gasoline or coal
–
Cars must have a catalytic converter, which helps ensure all C is converted to CO
2
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•
Effects of CO on humans
–
200-800 ppm leads to headache, fatigue, dizziness in a few hours
–
Death would occur under these conditions if exposed for several hours
–
1000 ppm exposure can lead to death in < 1 h
–
CO interferes with oxygen (O
2
) transport
–
The shape and size is about the same as O
2
–
Hemoglobin is tied up with CO
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•
Corrosion reactions can weaken structural metal
4 Fe + 3 O
2
----> 2 Fe
2
O
3
(rust)
•
Tarnishing of Silver
2 Ag + H
2
S ----> Ag
2
S + H
2
•
Removing tarnish from silver
2 Al + 3 Ag
2
S ----> 6 Ag + Al
2
S
3
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•
Ammonia Fertilizer
N
2
+ 3 H
2
----> 2 NH
3
Liquid ammonia is easily stored and applied (-33 o C)
Ammonia contains high nitrogen content
•
Vehicle Airbags
2 NaN3 ----> 2 Na + 3 N
2
Rapid formation of nitrogen gas inflates the airbag
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