1. Natural Approach to Chemistry Chapter 4 Physical and Chemical Change
4.1 Understanding Chemical Changes Frame 2-41
4.2 Chemical Reactions Frames 42-82
4.3 Chemical Reactions in the lab Frames

2. Physical and Chemical Change
CHAPTER 4
Physical and Chemical Change
4.1 Understanding Chemical Changes

3. Is it still the same substance? Have the physical properties changed?
H2O(s) H2O(l)
Is it still the same substance?
Have the physical properties changed?
4.1 Understanding Chemical Changes

4. Can water go back to being ice?
H2O(s) H2O(l) ?
Can water go back to being ice?
4.1 Understanding Chemical Changes

5. Is it still the same substance? Have the physical properties changed?
In the presence of a flame:
2C20H42(s) O2(g) H2O(g) CO2(g)
Is it still the same substance?
Have the physical properties changed?
4.1 Understanding Chemical Changes

6. Does the candle come back?
If the flame cools down:
Does the candle come back? ?
2C20H42(s) O2(g) H2O(g) CO2(g)
4.1 Understanding Chemical Changes

7. X The candle does not come back by itself.
If the flame cools down:
The candle does not come back by itself. X
2C20H42(s) O2(g) H2O(g) CO2(g)
In this chemical reaction, the atoms were rearranged.
This change is irreversible.
4.1 Understanding Chemical Changes

8. - the molecules are rearranged - intermolecular forces are broken
In a physical change:
- the molecules are rearranged
- intermolecular forces are broken
4.1 Understanding Chemical Changes

9. - the molecules are rearranged intermolecular forces are broken
In a physical change:
- the molecules are rearranged
intermolecular forces are broken
interatomic forces are not broken
In a chemical change:
- the atoms are rearranged
- interatomic forces are broken
4.1 Understanding Chemical Changes

10. Intermolecular forces.
Interatomic forces.
Intermolecular forces.
Intermolecular forces are much weaker than interatomic forces.
4.1 Understanding Chemical Changes

11. Physical or chemical change?
4.1 Understanding Chemical Changes

12. Physical or chemical change?
4.1 Understanding Chemical Changes

13. Physical or chemical change?
4.1 Understanding Chemical Changes

14. Physical or chemical change?
4.1 Understanding Chemical Changes

15. Can we obtain any arrangement of atoms?H H H
O2 (oxygen)
H2 (hydrogen)
H2O (water)
Can we obtain any arrangement of atoms? O H O H
H4O (?)
H3O (?)
4.1 Understanding Chemical Changes

16. Can we obtain any arrangement of atoms?H H H
O2 (oxygen)
H2 (hydrogen)
H2O (water)
Can we obtain any arrangement of atoms?
NO: each type of atom allows only certain chemical bonds to be formed
This is due to the structure of the atom
4.1 Understanding Chemical Changes

17. 99.8% of the mass of the atom is in the nucleus!
Structure of the Atom
An atom is not a hard ball. .
99.8% of the mass of the atom is in the nucleus!
4.1 Understanding Chemical Changes

18. .
The number of electrons corresponds to the atomic number of the element, as shown in the periodic table.
4.1 Understanding Chemical Changes

19. Electrons have a negative electric charge.
4.1 Understanding Chemical Changes

20. Electrons have a negative electric charge.
If negative charges repel each other,
how does an atom stay together?
4.1 Understanding Chemical Changes

21. Electrons have a negative electric charge.
Protons in the nucleus have a positive electric charge.
Proton: A tiny particle in the nucleus that has a positive charge.
Neutral: Having zero total electric charge.
4.1 Understanding Chemical Changes

22. Why don’t the negative electrons “fall” into the positive nucleus?
4.1 Understanding Chemical Changes

23. Because the electrons have energy and momentum
Why don’t the negative electrons “fall” into the positive nucleus?
Because the electrons have energy and momentum
- The same reason why the Earth does not fall into the sun, but gravitates around it instead.
4.1 Understanding Chemical Changes

24. Electrons are responsible for bond formation.
Electrons can be: - +
4.1 Understanding Chemical Changes

25. +1 -1 In ionic compounds, electrons are NOT SHARED but TRANSFERRED. ClNa
Sodium ion
Chloride ion
1 electron
Ionic bond Na Cl
Sodium atom
Chlorine atom
4.1 Understanding Chemical Changes

26. +2 -1 -1 In ionic compounds, electrons are NOT SHARED but TRANSFERRED.
Magnesium chloride (MgCl2) is also an ionic compound.
1 electron
1 electron +2 -1 Mg -1
Chloride ion Cl Cl
Chloride ion
Magnesium ion
Ionic bond
Ionic bond
Chloride atom Cl Mg
Chloride atom Cl
Magnesium atom
4.1 Understanding Chemical Changes

27. Covalent bonds
A chemical bond is formed by sharing or transferring electrons.
There are two covalent bonds in a water molecule.
Covalent bond: A chemical bond that consists of two shared electrons.
Molecule: A neutral group of atoms bonded together by covalent bonds.
4.1 Understanding Chemical Changes

28. Some elements can share multiple electrons with the same atom.
Multiple bonds
Single bonds
Double bond
Triple bond
Some elements can share multiple electrons with the same atom.
4.1 Understanding Chemical Changes

29. Lower energy = more stable
Chemical bonds form because there is an advantage in energy.
Lower energy =
more stable
4.1 Understanding Chemical Changes

30. Lower energy = more stable
Chemical bonds form because there is an advantage in energy.
Lower energy =
more stable
Enthalpy of formation
∆Hf (kJ/mole)
4.1 Understanding Chemical Changes

31. All chemical reactions involve three key components: Reactants
4.1 Understanding Chemical Changes

32. All chemical reactions involve three key components: Reactants
Products
Reactants
Products
4.1 Understanding Chemical Changes

33. All chemical reactions involve three key components: Reactants
Products
Reactants
Products
Energy (in or out)
Energy
4.1 Understanding Chemical Changes

34. Some elements are never found in pure form in nature:
Electrons are responsible for bonding among atoms.
Some elements are never found in pure form in nature:
Ex: Lithium (Li), sodium (Na)
Some elements are always found in pure form in nature:
Ex: Helium (He), argon (Ar) He
4.1 Understanding Chemical Changes

35. Some elements are more likely to react than others.
They are more reactive.
Reactivity: The tendency of elements to form chemical bonds.
4.1 Understanding Chemical Changes

36. Electrons make bonds. Electrons can be:
4.1 Understanding Chemical Changes

37. Can we predict if a compound is ionic or covalent?
4.1 Understanding Chemical Changes

38. Can we predict if a compound is ionic or covalent?
Yes!
Metal
Nonmetal
In an ionic compound,
one atom is a nonmetal, and one atom is a metal
4.1 Understanding Chemical Changes

39. Can we predict if a compound is ionic or covalent?
Yes!
Nonmetal
Nonmetal
In a covalent compound,
both atoms are nonmetals.
4.1 Understanding Chemical Changes

40. Use the periodic table to help determine whether a compound is ionic or molecular.
4.1 Understanding Chemical Changes

41. Is the compound CF4 ionic or molecular?
4.1 Understanding Chemical Changes

42. Is the compound CF4 ionic or molecular? Both nonmetals
4.1 Understanding Chemical Changes

43. Physical and Chemical Change
CHAPTER 4
Physical and Chemical Change
4.2 Chemical Reactions

44. Electrolysis ?
Experimental setup:
An electric current transfers a large amount of energy to water. ?
Observations:
The mass of water decreases over time.
The volume of gas increases.
4.2 Chemical Reactions

45. Electrolysis ?
Experimental setup:
An electric current transfers a large amount of energy to water. ?
Observations:
The mass of water decreases over time.
The volume of gas increases.
Hypothesis:
The gas produced is water vapor.
4.2 Chemical Reactions

46. Electrolysis ? ? The gas produced is water vapor.
Hypothesis:
The gas produced is water vapor. ?
Observations on the gases:
1. When cooled, the gas does not condense into liquid water.
2. One of the gases burns.
3. One of the gases causes a flame to get brighter.
4.2 Chemical Reactions

47. Electrolysis ? ? The gas produced is water vapor.
Hypothesis:
The gas produced is water vapor. ?
Observations on the gases:
1. When cooled, the gas does not condense into liquid water.
2. One of the gases burns.
3. One of the gases causes a flame to get brighter.
Conclusion:
The gas produced is not water vapor.
4.2 Chemical Reactions

48. Electrolysis ? ? One gas burns.
Clues:
One gas burns.
One gas causes a flame to get brighter.
The gases come from water. ? ?
4.2 Chemical Reactions

49. Electrolysis One gas burns. One gas causes a flame to get brighter.
Clues:
One gas burns.
One gas causes a flame to get brighter.
The gases come from water. +
4.2 Chemical Reactions

50. Chemical change: A result of chemical reaction.
The energy from the electric current was high enough to cause a chemical change through a chemical reaction. +
Chemical reaction: A process that rearranges the atoms in any substance(s) to produce one or more different substances.
Chemical change: A result of chemical reaction.
4.2 Chemical Reactions

51. +
A chemical equation
4.2 Chemical Reactions

52. The Chemical Equation oxygen oxygen hydrogen hydrogen
4.2 Chemical Reactions

53. How can we make both sides the same number of each atom?
The Chemical Equation ! 1 2
oxygen
oxygen 2 2
hydrogen
hydrogen
How can we make both sides the same number of each atom?
4.2 Chemical Reactions

54. The Chemical Equation oxygen oxygen hydrogen hydrogen
4.2 Chemical Reactions

55. The Chemical Equation 2 2 coefficients oxygen oxygen 4 4 hydrogen
4.2 Chemical Reactions

56. The Chemical Equation Reaction arrow Reactants Products Coefficients
2H2O(l) H2(g) O2(g)
Coefficients
Tell you how many of each molecule participate in the reaction
(No coefficient appears when it equals 1).
4.2 Chemical Reactions

57. The Chemical Equation 1. Determine if the equation is balanced.
Rules of balancing a chemical equation:
1. Determine if the equation is balanced.
Count the number of each kind of atom on either side of the arrow.
2. If it is not balanced, use coefficients.
Ex: H2O becomes 2H2O
3. Do not change the subscripts inside the molecular formulas.
Ex: H2O cannot become H3O
4. Check that the equation is balanced.
Count the number of each kind of atom on either side of the arrow with the new coefficients.
4.2 Chemical Reactions

58. Reactants Products Iron (Fe) Oxygen (O)
Is it balanced?
Reactants
Products
Iron (Fe)
Oxygen (O)
4.2 Chemical Reactions

59. 1 2 3 Reactants Products Iron (Fe) Oxygen (O) Is it balanced?
4.2 Chemical Reactions

60. 1 2 3 Reactants Products Iron (Fe) Oxygen (O) Not balanced
4.2 Chemical Reactions

61. The Chemical Equation 1. Determine if the equation is balanced.
Rules of balancing a chemical equation:
1. Determine if the equation is balanced.
Count the number of each kind of atom on either side of the arrow.
2. If it is not balanced, use coefficients.
Ex: H2O becomes 2H2O
3. Do not change the subscripts inside the molecular formulas.
Ex: H2O cannot become H3O
4. Check that the equation is balanced.
Count the number of each kind of atom on either side of the arrow with the new coefficients.
4.2 Chemical Reactions

62. Reactants Products Iron (Fe) Oxygen (O)
Add coefficients ? ? ?
Reactants
Products
Iron (Fe)
Oxygen (O)
4.2 Chemical Reactions

63. 4 6 4 3 2 Reactants Products Iron (Fe) Oxygen (O) Balanced!
4.2 Chemical Reactions

64. Photosynthesis is the basis of most life on Earth.
a sugar
(glucose)
gases
a gas
Photosynthesis is the basis of most life on Earth.
4.2 Chemical Reactions

65. Reactants Products Carbon (C) Oxygen (O) Hydrogen (H)
Verify that the equation is balanced
4.2 Chemical Reactions

66. Number of atoms or moles
Verify that the equation is balanced
Reactants
Products
Carbon (C) 6
Oxygen (O) 18
Hydrogen (H) 12
Number of atoms or moles
4.2 Chemical Reactions

67. Use the formula mass to convert from moles to grams.
4.2 Chemical Reactions

68. Total mass of reactants Total mass of products
108 g
+ 264 g
372 g
180 g
+ 192 g
372 g
4.2 Chemical Reactions

69. Conservation of mass Total mass of reactants Total mass of products
108 g
+ 264 g
372 g
180 g
+ 192 g
372 g
Conservation of mass
4.2 Chemical Reactions

70. Total mass of reactants = Total mass of products
Conservation of mass: Law that states that, in any chemical reaction, the total mass remains the same.
Total mass of reactants = Total mass of products
4.2 Chemical Reactions

71. All chemical reactions involve three key components:
Reactants
Products
Reactants
Products
Energy (in or out)
Energy
4.2 Chemical Reactions

72. Energy “in” An endothermic reaction requires an input of energy.
Energy as a reactant.
reactants
products
An endothermic reaction requires an input of energy.
4.2 Chemical Reactions

73. Energy “out” An exothermic reaction releases energy.
Energy as a product.
reactants
products
An exothermic reaction releases energy.
4.2 Chemical Reactions

74. Energy is absorbed
Energy is released
4.2 Chemical Reactions

75. First law of thermodynamics:
Energy can neither be created nor destroyed.
Energy is absorbed
Are these violations of the first law?
Energy is released
4.2 Chemical Reactions

76. First law of thermodynamics:
Energy can neither be created nor destroyed.
4.2 Chemical Reactions

77. What is missing? Mixing water and CO2 doesn’t make
Photosynthesis
Mixing water and CO2 doesn’t make
sugar and O2 because energy input is needed.
Respiration
Energy input is
not needed
but just mixing sugar and O2 doesn’t make
water and CO2.
4.2 Chemical Reactions

78. What is missing? A candle burning gives off heat.
It is an exothermic reaction.
However, the candle does not spontaneously light itself up.
4.2 Chemical Reactions

79. What is missing? A candle burning gives off heat.
It is an exothermic reaction.
However, the candle does not spontaneously light itself up.
4.2 Chemical Reactions

80. Activation energy C6H12O6 + 6O2 6H2O + 6CO2 + 2,800,000J
4.2 Chemical Reactions

81. Activation energy C6H12O6 + 6O2 6H2O + 6CO2 + 2,800,000J
4.2 Chemical Reactions

82. Activation energy C6H12O6 + 6O2 6H2O + 6CO2 + 2,800,000J
4.2 Chemical Reactions

83. Activation energy C6H12O6 + 6O2 6H2O + 6CO2 + 2,800,000J
an energy barrier!
4.2 Chemical Reactions

84. Physical and Chemical Change
CHAPTER 4
Physical and Chemical Change
4.3 Chemical Reactions in the Lab

85. Why would the presence of water on Mars be a sign that life might exist there?
4.3 Chemical Reactions in the Lab

86. Why would the presence of water on Mars be a sign that life might exist there?
Many reactions,
including those that sustain life, involve chemicals dissolved in water.
4.3 Chemical Reactions in the Lab

87. DRY
Light blue powder
No reaction
4.3 Chemical Reactions in the Lab

88. No reaction Chemical reaction DRY IN SOLUTION NaS(aq) CuSO4(aq)
Light blue powder
NaS(aq) CuSO4(aq)
No reaction
Chemical reaction
A precipitate is an insoluble compound.
4.3 Chemical Reactions in the Lab

89. A solution with water as the solvent is called an aqueous solution.
“Aqua” means “water”
A solution with water as the solvent is called an aqueous solution.
SYMBOLS
(s) indicates a solid
(l) indicates a liquid
(g) indicates a gas
(aq) indicates a substance dissolved in water (an aqueous solution)
4.3 Chemical Reactions in the Lab

90. O H S O Cu S O 2- 2+ Cu O H
A salt is an ionic compound that forms ions when dissolved in water. O H O H
4.3 Chemical Reactions in the Lab

91. Can you translate what you see into a chemical equation?
4.3 Chemical Reactions in the Lab

92. Can you translate what you see into a chemical equation?
Cu(s)
Zn(s) CuSO4(aq)
and Zn(s) is disappearing
4.3 Chemical Reactions in the Lab

93. Can you translate what you see into a chemical equation?
Cu(s)
Zn(s) CuSO4(aq)
and Zn(s) is disappearing
a salt in water!
4.3 Chemical Reactions in the Lab

94. Can you translate what you see into a chemical equation?
Cu2+(aq)
SO42-(aq)
Cu(s)
Zn(s) +
and Zn(s) is disappearing
4.3 Chemical Reactions in the Lab

95. Cu2+(aq)
SO42-(aq)
Cu(s)
Zn(s) +
and Zn(s) is disappearing
Cu2+(aq) e Cu(s)
The copper ion gains 2 electrons to form solid copper.
Reduction: A chemical reaction that decreases the charge of an atom or ion by accepting electrons.
4.3 Chemical Reactions in the Lab

96. Where could those electrons come from?
Cu2+(aq)
SO42-(aq)
Cu(s)
Zn(s) +
and Zn(s) is disappearing
Cu2+(aq) e Cu(s)
The copper ion gains 2 electrons to form solid copper.
Where could those electrons come from?
4.3 Chemical Reactions in the Lab

97. Cu2+(aq) + 2e- Cu(s) Zn(s) Zn2+(aq) + 2e-
SO42-(aq)
Cu(s)
Zn(s) +
and Zn(s) is disappearing
Cu2+(aq) e Cu(s)
Zn(s) Zn2+(aq) e-
Zinc gives up 2 electrons to become a zinc ion, dissolved in water.
4.3 Chemical Reactions in the Lab

98. Oxidation: A chemical reaction that increases the charge of an atom or ion by giving up electrons.
Zn(s) Zn2+(aq) e-
Zinc gives up 2 electrons to become a zinc ion, dissolved in water.
4.3 Chemical Reactions in the Lab

99. Cu2+(aq) + 2e- Cu(s) reduction REACTION NAME Reactants Products
4.3 Chemical Reactions in the Lab

100. Cu2+(aq) + 2e- Cu(s) reduction Zn(s) Zn2+(aq) + 2e- oxidation
REACTION NAME
Reactants
Products
Cu2+(aq) e Cu(s)
reduction
Zn(s) Zn2+(aq) e-
oxidation
4.3 Chemical Reactions in the Lab

101. To obtain the overall reaction add the reactants, then the products.
REACTION NAME
Reactants
Products
Cu2+(aq) e Cu(s)
reduction
Zn(s) Zn2+(aq) e-
oxidation
These 2 reactions are happening at the same time.
To obtain the overall reaction
add the reactants, then the products.
4.3 Chemical Reactions in the Lab

102. Cu2+(aq) + Zn(s) Cu(s) + Zn2+(aq) redox
REACTION NAME
Reactants
Products
Cu2+(aq) e Cu(s)
reduction
Zn(s) Zn2+(aq) e-
oxidation
Cu2+(aq) Zn(s) Cu(s) Zn2+(aq)
redox
4.3 Chemical Reactions in the Lab

103. - + H2O OH- + H+ dissociation O O H H H
The double arrow indicates that the reaction goes in both ways.
The heavier arrow means that the reverse reaction is favored.
4.3 Chemical Reactions in the Lab

104. Classify these items as acids or bases.
4.3 Chemical Reactions in the Lab

105. HCl(l) H+(aq) + Cl-(aq)
Acids give foods like lemons their sour taste.
Acids react with metal to create hydrogen gas (H2).
Acids can corrode metal and burn skin.
Example:
H2O(l)
HCl(l) H+(aq) Cl-(aq)
Hydrochloric acid
Acid: A chemical that dissolves in water to create more H+ ions than there are in neutral water.
4.3 Chemical Reactions in the Lab

106. NaOH(l) Na+(aq) + OH-(aq)
Bases create a bitter taste.
Bases have a slippery feel, like soap.
Bases can neutralize acids.
Example:
H2O(l)
NaOH(l) Na+(aq) OH-(aq)
Sodium hydroxide
4.3 Chemical Reactions in the Lab

107. NaOH(l) Na+(aq) + OH-(aq)
Bases create a bitter taste.
Bases have a slippery feel, like soap.
Bases can neutralize acids.
Example:
H2O(l)
NaOH(l) Na+(aq) OH-(aq)
Sodium hydroxide
OH-(aq) H+(aq) H2O(l)
Result: fewer H+ ions
4.3 Chemical Reactions in the Lab

108. NaOH(l) Na+(aq) + OH-(aq)
Base: A chemical that dissolves in water to create fewer H+ ions (or more OH- ions)than there are in neutral water.
Example:
H2O(l)
NaOH(l) Na+(aq) OH-(aq)
Sodium hydroxide
OH-(aq) H+(aq) H2O(l)
Result: fewer H+ ions
4.3 Chemical Reactions in the Lab

109. 4.3 Chemical Reactions in the Lab

110. Higher H+ concentration Lower H+ concentration
The pH scale helps to determine whether a solution is acidic or basic.
4.3 Chemical Reactions in the Lab