CHEMICAL REACTIONS

1
CHEMICAL REACTIONS

• Chapter 7

2
Changes

• PHYSICAL
• Only affects the size, shape and state.
• Amount of energy involved in each state varies.

• CHEMICAL
• Atoms are rearranged.
• Bonds broken
• new substance created
• Energy released or absorbed

3
Physical OR Chemical Reactions?
4
Lab Conservation of MassPhysical or Chemical
Change?

• A Dissolving Salt and Water
• B Melting Ice
• C Lead nitrate mixed with sodium chloride OR
  sodium iodide
• D copper and sulfur
• E water and alka-seltzer

5
Lab Conservation of MassPhysical or Chemical
Change?

• A Dissolving Salt and Water
• B Melting Ice
• C Lead nitrate mixed with sodium chloride OR
  sodium iodide
• D copper and sulfur
• E water and alka-seltzer

• Physical
• Physical
• Chemical
• Chemical
• Chemical

6

• Chemical Reactions Rearrange atoms

REACTANTS PRODUCTS C2H5OH 3O2 2CO2
3H2O New product atoms and old reactant atoms are
not created or destroyed. Mass is always
conserved.
7
Energy and Reactions

• Energy must be added to break bonds
• Energy
• Heat
• Electricity
• Sound
• light

8
Energy and Reactions

• Forming bonds releases energy

9
Energy and Reactions
10
Examples

• Endothermic
• Photosynthesis
• Dissolving most salts into water (exceptions)
• Decomposition reactions        A gt B C

• Exothermic
• Combustion of Methane (Natural Gas).
• Adding concentrated sulfuric acid to water
• Acid/Base reactions        Dissolving a strong
  acid or strong base

11
Diatomic Molecules

• Most elemental gases do not exist as single atoms
  
• H2
• N2
• F2
• O2
• I2
• Cl2
• Br2

12
7.2 Chemical Reactions Are Represented by
Chemical Equations
13
Chemical Equation
A representation in which reactants are written
before an arrow and products are written after
the arrow.
14
Reactants
Products
15
Reactants
Substances that are about to chemically react.
16
Products
Substances that are formed from a chemical
reaction.
17
Animation
CO2flask.mov
18
Reactants
19
Carbon,C
Reactants
20
Carbon,C
Oxygen, O2
Reactants
21
Chemical reaction
22
Products
23
Carbon Dioxide, CO2
Products
24
Coefficients
Integers used to indicate the ratio by which
reactants react and products form.
25
H2
O2
H2O

Reactants
Products
26
H2
O2
H2O
2

Reactants
Products
27
H2
O2
H2O
2
1

Reactants
Products
28
H2
O2
H2O
2
1
2

Reactants
Products
29
H2
O2
H2O
2
2

Reactants
Products
30
H2
O2
H2O
2
2
(g)
(g)
(g)

Reactants
Products
31
Balancing Chemical Equations
32
Balancing Guidelines

• Balance one element at a
• time.

2) If you incidentally unbalance an element
leave it alone.
3) Make successive passes.
33
Al2O3
C
CO2
Al


34
Al2O3
C
CO2
Al


(not balanced)
35
Al2O3
C
CO2
Al


36
Al2O3
C
CO2
Al


Al
Al
C
Al
C
O
O
O
O
O
37
Al2O3
C
CO2
Al


38
2
Al2O3
C
CO2
Al


39
2
Al2O3
C
CO2
Al


Al
Al
Al
C
C
O
O
O
O
O
Al
40
2
Al2O3
C
CO2
Al


41
2
3
2
Al2O3
C
CO2
Al


42
2
3
2
Al2O3
C
CO2
Al


C
O
O
Al
Al
Al
O
O
O
C
C
O
O
Al
C
O
O
Al
Al
O
O
O
43
2
3
2
Al2O3
C
CO2
Al


44
2
3
2
3
Al2O3
C
CO2
Al


45
2
3
2
3
Al2O3
C
CO2
Al


C
O
O
C
Al
Al
Al
O
O
O
C
C
O
O
Al
C
C
O
O
Al
Al
O
O
O
46
Balanced
4
3
2
3
Al2O3
C
CO2
Al


C
O
O
C
Al
Al
Al
O
O
O
C
C
O
O
Al
Al
C
C
O
O
Al
Al
Al
O
O
O
47
Balanced
4
3
2
3
Al2O3
C
CO2
Al


48
not balanced
Na2SO3
S8
Na2S2O3

49
Na2SO3
S8
Na2S2O3

50
1
1
Na2SO3
S8
Na2S2O3

51
1
1
Na2SO3
S1
Na2S2O3

52
1
1
Na2SO3
S8
Na2S2O3

53
1
1
1
Na2SO3
S8
Na2S2O3

8
54
1
1
1
Na2SO3
S8
Na2S2O3

8
S
S
S
S
S
S
S
S
55
1
1
1
Na2SO3
S8
Na2S2O3

8
S
S
S
S
S
S
S
S
56
1
1
1
Na2SO3
S8
Na2S2O3

8
S
S
S
S
S
S
S
S
57
1
1
1
Na2SO3
S8
Na2S2O3

8
S
S
S
S
S
S
S
S
58
1
1
1
Na2SO3
S8
Na2S2O3

8
59
1
1
1
Na2SO3
S8
Na2S2O3

8
60
1
8
1
1
Na2SO3
S8
Na2S2O3

8
61
1
8
x
8
8
8
Na2SO3
S8
Na2S2O3

62
1
8
x

1
8
8
8
Na2SO3
S8
Na2S2O3

63
8
8
1
Na2SO3
S8
Na2S2O3

64
Balanced
8
8
1
Na2SO3
S8
Na2S2O3

65
7.1 Chemical Reactions Are Represented by
Chemical Equations
66
7.2 Chemists Use Relative Masses to Count
Atoms and Molecules
67
TYPES OF REACTIONS

• Chapter 7

68
Types of Reaction

• 1. Addition Reactions (aka synthesis)
• A B AB
• 2 or more substances combine to form a new
  compound.
• small molecules join to form chains -
• polymerization
• Fe O2 Fe2O3

69
Types of Reactions

• 2. Decomposition Reactions
• AB A B
• compounds are broken apart into smaller
  substances
• Example Electrolysis of water
• 2 H2O 2 H2 O2

70
Types of Reactions

• Single Displacement Reaction
• AX B BX A
• One element replaces a similar element in a
  compound
• Aka Single Replacement Reaction

71
Types of Reactions

• Double Displacement Reaction
• AB CD AD CB
• Aka double replacement reactions
• Ions from 2 compounds in solution exchange places
  to produce 2 new compounds.
• One of the compounds is usually
• A precipitate
• A gas that bubbles off
• A molecular compound like water

72
Types of Reactions

• Combustion Reactions
• These use O2 as a reactant
• One product contains O and the other usually H2O
• Carbon cpd. O2 CO2 H2O
• __________________________________________________
  __________________________________________________
  _______________

73
Types of Reactions

• Combustion Reactions
• These use O2 as a reactant
• One product contains O , usually H2O
• __________________________________________________
  __________________________________________________
  ________________________
• Importance of Good Air Supply
• 2CH4 4O2 2CO2 4H2O
• 2CH4 3O2 2CO 4H2O
• 2CH4 2O2 2C 4H2O

74
Chapter 7.1 Energy in Reactions
75
Examples

• Endothermic
• Melting of ice
• evaporation of water
• boiling of water.
• Photosynthesis
• Dissolving most salts into water (exceptions)
• Decomposition reactions        AB gt A B

• Exothermic
• Combustion of Methane (Natural Gas).
• Adding concentrated sulfuric acid to water
• Acid/Base reactions        Dissolving a strong
  acid or strong base

76
Other Terms - refers to the ease in which the
reactions occurs

• Exergonic
• Most cases are exothermic
• Bioluminescence
• Respiration

• Endergonic
• Most cases are endothermic
• Photosynthesis

77
Endothermic Reaction (ex. Photosynthesis) takes
in energy- cold pack Exothermic Reactions (ex.
Cell Respiration) gives off energy hot pack
Plus more balancing reactions to show
conservation of mass and energy
78
             860 691 - fphoto.photoshelter.com
             605 500 - fphoto.com
__Cu__O2?__CuO __Cu__S?__CuS H2O ? 2H2 O2
CuCl2 Zn ? ZnCl2 Cu HCl NaOH ? HOH
NaCl PbNO3 KI ? PbI KNO3 PbNO3NaCl?PbCl
NaNO3
4CH3 7O2 ?4CO2 6H2O
79
             448 420 - witcombe.sbc.edu
2CuO2?2CuO or CuS?CuS __H2O ? __H2 __O2
CuCl2 Zn ? ZnCl2 Cu HCl NaOH ? HOH
NaCl PbNO3 KI ? PbI KNO3 PbNO3NaCl?PbCl
NaNO3
4CH3 7O2 ?4CO2 6H2O
80
2CuO2?2CuO or CuS?CuS 2H2O ? 2H2 O2 __CuCl2
__Zn ? __ZnCl2 __Cu HCl NaOH ? HOH
NaCl PbNO3 KI ? PbI KNO3 PbNO3NaCl?PbCl
NaNO3
4CH3 7O2 ?4CO2 6H2O
81
2CuO2?2CuO or CuS?CuS 2H2O ? 2H2 O2 CuCl2
Zn ? ZnCl2 Cu __HCl __NaOH ? __HOH
__NaCl __PbNO3 __KI ? __PbI
__KNO3 __PbNO3__NaCl?__PbCl __NaNO3
4CH3 7O2 ?4CO2 6H2O
82
2CuO2?2CuO or CuS?CuS 2H2O ? 2H2 O2 CuCl2
Zn ? ZnCl2 Cu HCl NaOH ? HOH NaCl PbNO3
KI ? PbI KNO3 PbNO3NaCl?PbCl NaNO3
__CH4 __O2 ?__CO2 __H2O
83
Examples

• Endothermic
• Melting of ice
• evaporation of water
• boiling of water.
• Photosynthesis
• Dissolving most salts into water (exceptions)
• Decomposition reactions        A gt B C

• Exothermic
• Combustion of Methane (Natural Gas).
• Adding concentrated sulfuric acid to water
• Acid/Base reactions        Dissolving a strong
  acid or strong base