1. Chapter 7
Chemical Reactions

2. Homework Assigned Problems (odd numbers only)
“Questions and Problems” to 7.31 (begins on page 200)
“Additional Questions and Problems” to 7.49 (page 221)
“Challenge Questions” (page 222)

3. Evidence of a Chemical Reaction
Physical changes:
Involves no changes in chemical identity of a substance
No changes in physical properties (color, physical state, freezing point, boiling point)
Chemical changes:
A chemical reaction in which one or more substances changes to a different substance
Properties that matter exhibits as it undergoes changes in chemical composition

4. Evidence of a Chemical Reaction
As a result of the chemical change, a chemical reaction has occurred which produces at least one new substance
Changes that identify chemical reactions (visual clues)
color change
precipitate formation
gas bubbles
flames
heat release

5. Evidence of a Chemical Reaction
A chemical change is a process that causes a change in the chemical composition of a substance
The creation of one or two new substances is characteristic of a chemical change
A chemical change occurs when new substances are made
Conversion of material(s) into one or more new substances
These substances will have different properties from the original material

6. Evidence of a Chemical Reaction
Fe Fe2O3
Li LiOH, H2
HCO CO2
Lithium reacts with water to generate lithium hydroxide and hydrogen gas
Bicarbonate ion reacting with water to generate carbon dioxide
Na NaOH, H2

7. The Chemical Equation
Chemical properties determine whether or not a substance can be changed to another substance
Chemical Reactions:
are processes that involve chemical changes in matter resulting in new substances
involve a rearrangement and exchange of atoms to produce new molecules
Elements are not changed during a reaction
Chemists have developed a shorthand way of stating chemical changes on paper: The chemical equation
Chemical properties determine whether or not a substance can be changed into another substance. The arrow indicates the direction of chemical change.

8. The Chemical Equation Reactants  Products
A chemical equation is a written statement that uses symbols and formulas (or words) to describe the changes during a chemical reaction
It shows substances at the beginning of a reaction (reactants)
It shows substances formed in the reaction (products)
The reactants and products are separated by an arrow
It is an abbreviated way of representing a chemical reaction on paper
Reactants  Products

9. The Chemical Equation For a chemical equation to be valid:
Only the reactants and products involved in the reaction are shown in the equation
The accurate formulas must be used for each of the substances
The law of conservation of mass must be obeyed: Equal numbers of the same kind of atom on the reactant and product side of the equation
It must be consistent with the experimental facts. Molecular, not empirical formulas always used. Equation must be balanced.

10. The Chemical Equation
The law of conservation of mass is complied with:
Matter is not created nor destroyed during a chemical reaction
At least one new substance is produced but the quantity of matter does not change
Every atom present as a reactant has to be present as a product
The sum of the masses of the products is always equal to the sum of the masses of the reactants
From the result of a chemical reaction (during the process)
bonds in the reactants are broken, atoms rearrange and reform into products

11. How to Write Balanced Chemical Equations
A balanced chemical reaction has the same number of atoms of each element involved on each side of the equation
A balanced equation is consistent with the law of conservation of mass
Chemical reactions can be written as:
Word equations
Formula equations
Word equations use the chemical names of the reactants and products
Formula equations use symbols and formulas of the substances involved
reactants
products

12. How to Write Balanced Chemical Equations
A balanced chemical reaction has the same number of atoms of each element on both sides of the arrow
Every atom must be accounted for (atoms are neither created nor destroyed)
Equations are balanced by placing a coefficient in front of one or more of the substances in the equation
A chemical reaction obeys the Law of Conservation of Mass
If there are 10 carbon atoms in the reactants, there must be 10 carbon atoms in the reactants

13. How to Write Balanced Chemical Equations Symbols Used in Equations
To convey more information than just the type of chemical involved, symbols are used after a chemical formula to indicate its physical state
(g) = gas
(l) = liquid
(s) = solid
(aq) = aqueous, dissolved in water

14. How to Write Balanced Chemical Equations
When magnesium metal burns in air it produces a white, powdery compound: magnesium oxide
Burning in air means reacting with O2
Write the word equation
The reactants are to the left of the arrow
The products are to the right of the arrow
Two or more reactants or products are separated by a plus sign
A word description
Reactants on the left and products on the right, separated by an arrow
magnesium + oxygen magnesium oxide

15. How to Write Balanced Chemical Equations
Indicate the physical state of each substance
Use the correct chemical symbol to indicate liquids and solids
Metals are solids, except for Hg which is liquid
Use molecular form for gases (H2, O2, N2, all halogens)
Identify polyatomic ions
Elements in the solid and liquid states are represented in equations by the chemical symbols for the element
magnesium(s) + oxygen(g) magnesium oxide(s)

16. How to Write Balanced Chemical Equations
Convert the word equation into a formula equation
Use the correct chemical symbol to indicate liquids and solids
There must be the same number of each kind of atom on the reactant and product side of the equation
Determine if the equation is balanced
If not equal, must BALANCE
Elements in the solid and liquid states are represented in equations by the chemical symbols for the element
The arrow means “to produce”
Always use molecular not empirical formulas
Use the correct chemical symbol for the elements
Elements that are gases at room temperature are identified by their correct molecular form
___Mg (s) +___O2 (g) ___MgO(s)

17. How to Write Balanced Chemical Equations
Unbalanced equations can be adjusted by the use of a coefficient placed to the left of a substance
Coefficients will adjust the number of reactant and/or products molecules or formula units
NEVER change the subscripts of a compound to balance an element
It changes the identity of the compound
Can change coefficients but never subscript numbers
Adding coefficients to the equation will adjust the number of reactant and or product molecules
A coefficient will denote the amount of a substance

18. How to Write Balanced Chemical Equations
Guidelines when writing balancing chemical equations
Write the unbalanced chemical equation
Pick the element that occurs in only one compound on both sides of the equation
The element that occurs as a free element on either side of the equation, balance it last

19. Balancing a Chemical Equation Example 12 2
Coefficient 2
1 Mg 2
1 Mg
2 O 2
1 O
The coefficient affects both of the elements

20. Balancing a Chemical Equation: Example 2
When solid ammonium nitrite is heated it produces nitrogen gas and water vapor
Write the formula equation

21. Balancing a Chemical Equation Example 2
2 x N
2 x N
2 x O 2
1 x O
4 x H 4
2 x H

22. Balancing a Chemical Equation: Example 3
Nitrogen monoxide gas decomposes to produce dinitrogen monoxide gas and nitrogen dioxide gas
Write the formula equation

23. Balancing a Chemical Equation Example 3
1 x N
3 x N 3
1 x O
3 x O

24. Balancing a Chemical Equation Example 4
Liquid nitric acid decomposes to reddish-brown nitrogen dioxide gas, liquid water and oxygen gas.
Write the formula equation

25. Balancing a Chemical Equation Example 42 2 2 4 2
1 x N 4 2
1 x N 12 6
3 x O 12 7
5 x O 4 2
1 x H 4
2 x H

26. Aqueous Solutions and Solubility: Compounds Dissolved in Water
An aqueous solution:
A homogeneous mixture of a substance with water
It contains one visible phase, cannot differentiate the various components
Same composition throughout with one substance dissolved into another
A uniform mixture requires complete interaction of the components

27. Aqueous Solutions and Solubility: Compounds Dissolved in Water
Two parts: Solvent and Solute
Solute: Substance being dissolved
Solvent: Substance that dissolves the solvent
Most solutions are liquid but can be gaseous or solid
Can have more than one solute, but only one solvent

28. Aqueous Solutions and Solubility: Compounds Dissolved in Water
Water is an effective solvent for dissolving ionic compounds
Water is neutral but the O atom is surrounded by many electrons and gives it a partial negative charge
The other end which contains the H atom has a partial positive charge
The positive ions are attracted to the O atom and negative ions to the H atom of water
As an ionic compound dissolves, it becomes surrounded by water molecules

29. Aqueous Solutions and Solubility: Compounds Dissolved in Water
When sodium chloride crystals are placed in water, they begin to dissolve
The attractive forces between the ions and water are stronger than forces between the ions in the crystal
Water molecules surround each ion, keeping them apart
The ions become uniformly dispersed throughout the solution
Cliff page 359, figure 12.2 text

30. Aqueous Solutions and Solubility: Compounds Dissolved in Water
When ionic compounds dissolve in water the ions dissociate and separate into ions floating in water
Potassium chloride dissociates in water into potassium cations and chloride anions
KCl(aq) = K+ (aq) + Cl- (aq) K+
Cl- K Cl

31. Aqueous Solutions and Solubility: Compounds Dissolved in Water
Copper(II) sulfate dissociates in water into copper(II) cations and sulfate anions
CuSO4(aq) = Cu+2(aq) + SO42-(aq)
Cu+2
SO42- Cu
SO4

32. Aqueous Solutions and Solubility: Compounds Dissolved in Water
Potassium sulfate dissociates in water into potassium cations and sulfate anions
K2SO4(aq) = 2 K+ (aq) + SO42-(aq) K+
SO42- K
SO4

33. Electrolytes and Nonelectrolytes
A substance that exists as ions in solution
Formed from an ionic compound that dissociates in water forming a solution with cations and anions
Strong electrolytes are ionic compounds that dissociate (nearly) completely in solution and exist as ions
Strong electrolyte solutions conduct electricity due to the presence of ions

34. Electrolytes and Nonelectrolytes
Solute is a molecular substance (not ionic)
It does not form ions in solution (no dissociation)
Substance remains intact, dispersed throughout the solvent as individual molecules
Each molecule is separated by molecules of the solvent
These substances do not conduct electricity

35. Electrolytes and Nonelectrolytes
Strong electrolyte:
Dissociates completely into ions
Conducts electricity
NaCl, HCl
Weak electrolyte:
Mainly whole molecules
Very few separate (into ions)
Conducts electricity less than strong electrolytes
Acetic acid, HF
Nonelectrolyte:
No dissociation into ions
Do not conduct electricity
Methanol, sucrose

36. Electrolytes and Nonelectrolytes
Strong electrolytes are completely ionized when dissolved in water
Sodium chloride dissociates to form Na+ and Cl-
Good conductor of electricity
Show Timberlake page 380 and Zumdahl pg 135

37. Electrolytes and Nonelectrolytes
Weak electrolytes are only partially ionized when dissolved in water
Hydrofluoric acid only partially dissociates to form H+ and F-
Poor conductor of electricity
Show Timberlake page 380 and Zumdahl pg 135

38. Electrolytes and Nonelectrolytes
Nonelectrolyes are not ionized when dissolved in water
e.g. sugar and ethanol do not dissociate into ions in water
Do not conduct electricity
Molecules remain intact
Show Timberlake page 380 and Zumdahl pg 135

39. Solubility: Soluble and Insoluble Salts
Not all ionic compounds are soluble in water
If water cannot overcome the ionic forces to separate the ions in solution: insoluble compound
The factors to determine solubility are complex which make predictions difficult
Through observation a series of statements or rules have developed to guide predictions called the solubility rules (See Table 7.2, page 210 and handout)
For all solid in liquid solutions, all ionic compounds do not dissolve in water. Even if it is polar, “like dissolves like” does not always apply.
As the size of the charges on the cation and anion become larger, the forces holding the crystal together become so great that they cannot be overcome

40. Solubility Rules
Most compounds that contain NO3- and C2H3O2- ions are soluble in water
Most compounds that contain Li+, Na+, K+, or NH4+ ions are soluble in water
Most compounds that contain Cl-, Br-, I- ions are soluble, except AgCl, PbCl2, and Hg2Cl2
Most compounds that contain SO42- ions are soluble, except SrSO4, BaSO4, PbSO4, CaSO4
Solubility rules for ionic compounds in water

41. Solubility Rules
Most compounds that contain OH- ions are slightly soluble (will precipitate).
Exceptions: NaOH, KOH, are soluble and
Ba(OH)2, Ca(OH)2 are moderately soluble
Most compounds that contain S2-, CO32-, or PO43- ions are slightly soluble (will precipitate)

42. Precipitation Reactions
Upon mixing two aqueous solutions, if two ions of an insoluble salt come into contact, a solid forms
This is a precipitation reaction
The solid that forms is called a precipitate
Can use the solubility rules to predict whether a solid will form when two ionic solutions are mixed

43. Precipitation Reactions
Two aqueous clear solutions are mixed together: lead (II) nitrate and potassium iodide
The reaction between two solutes produces an insoluble product: lead (II) iodide

44. Predicting Precipitation Reactions
There are no simple (basic) rules to predict which ionic compounds will be insoluble
Experimental observations have led to the guidelines for predicting solubility (see text: table 7.2, page 210 and handout)
These solubility rules will be used to predict the products formed in precipitation reactions

45. Predicting Precipitation Reactions
In solution, the cations of the two reactants exchange anions
The chemical formulas are based on the charges on the ions
Will the new interactions of cations and anions form an insoluble compound?

46. Predicting Precipitation Reactions
To predict the identities of the products:
Write the formulas of the two compounds being mixed as reactants in a chemical equation
Separate all soluble ionic compounds into ions
AB + CD
A+ B C+ D-
Reactants

47. Predicting Precipitation Reactions
Write the formulas of the potentially insoluble products that could form from the new combination of the ions
Exchange pairs
Charge balance each compound
A B-
C D-
A+ D C+ B-
Products

48. Predicting Precipitation Reactions
Use the solubility rules to determine whether any of the new products are insoluble
If all of the potentially insoluble products are soluble, there will be no precipitate (NO REACTION)
If any of the potential products are insoluble, use symbol (s) to indicate a solid forms
Balance the equations with coefficients

49. Writing Equations for Precipitation Reactions
Aqueous solutions of calcium chloride and sodium carbonate are mixed
Write the formula of the two compounds
Write the formulas of the potentially insoluble products that could form from the reactants
Ca2+
2 Cl-
2 Na+
CO32-

50. Writing Equations for Precipitation Reactions
Use the solubility rules to determine whether any of the new products are insoluble
NaCl is soluble (Rule 2, Rule 3)
CaCO3 is insoluble (Rule 6)
Since one of the potential products is insoluble, write the formulas of the products of the reaction

51. Writing Equations for Precipitation Reactions
Include the symbol (s) to indicate solid and (aq) to indicate aqueous products
Balance the equation
Use coefficients, do not change the subscripts 2

52. Molecular, Complete Ionic, and Net Ionic Equations
Example
Two aqueous clear solutions are mixed together: lead (II) nitrate and potassium iodide
The reaction between two solutes produces an insoluble product: lead (II) iodide

53. Molecular, Complete Ionic, and Net Ionic Equations
Molecular Equations
Equations which show the complete chemical formulas for all reactants and products
Uses neutral formulas or symbols without indicating ionic character

54. Molecular, Complete Ionic, and Net Ionic Equations
Complete Ionic Equations
Separates the neutral formulas into the ions they will actually form in solution
Equations which describe the actual ions and molecules in the solutions as well as the molecules of solid, liquid and gas not dissolved
Notice that the potassium ion and the nitrate ion remain unchanged even as product is formed

55. Molecular, Complete Ionic, and Net Ionic Equations
Spectator Ions
Ions that appear in identical forms on both sides of the equation
Although present, they play no role in the reaction
Net Ionic Equation
An ionic equation in which the spectator ions are omitted
It shows only the ions that are directly involved in a chemical reaction

56. Predicting Reactions
When chemicals (dissolved in water) are mixed and one of these four events can occur, the reaction will generally happen
“Forces” that drive a reaction
formation of a solid
formation of water
transfer of electrons
formation of a gas

57. Predicting Reactions Determine if product(s) are:
Insoluble (precipitation reaction)
Water (acid/base reaction)
Electron transfer (redox reaction)
Gas (gas-forming reaction)

58. Acid-Base (Neutralization) Reactions
Acids are substances that form H+ ion in water
Bases are substances that form OH- ion in water
A Neutralization reaction is the reaction between an acid and a hydroxide base to form a salt and water

59. Acid-Base (Neutralization) Reactions
The reaction of hydrochloric acid and sodium hydroxide:
A double replacement reaction
Ionic Equation (remove spectator ions)
Net Ionic Equation (water forms)
acid
base
salt
water
Heat of formation of water generates heat

60. Predicting Reactions Determine if product(s) are:
Insoluble (precipitation reaction)
Water (acid/base reaction)
Electron transfer (redox reaction)
Gas (gas-forming reaction)

61. Gas Evolution Reactions
Other anions that will react with H+ are sulfide, carbonate, and bicarbonate ion
These anions react with acids to form gases
Sulfuric acid reacting with aqueous lithium sulfide
Molecular equation
acid
base
gas
salt

62. Gas Evolution Reactions
Complete ionic equation
Net ionic equation
(balanced)

63. Predicting Reactions Determine if product(s) are:
Insoluble (precipitation reaction)
Water (acid/base reaction)
Electron transfer (redox reaction)
Gas (gas-forming reaction)

64. Oxidation-Reduction Reactions
When an atom, ion, or molecule becomes more positively charged, a loss of electrons occurs: oxidation
When an atom, ion, or molecule becomes more negatively charged, a gain of electrons occurs: reduction
When one reactant loses electrons another reactant must gain electrons
Reactions in which this electron transfer occurs between reactants is called an oxidation-reduction (redox) reaction

65. Oxidation-Reduction Reactions
A substance reacting with elemental oxygen
A metal reacting with a nonmetal
Electron transfer between two reactants
Be able to identify these types of redox reactions

66. Combustion Reactions
Combustion occurs when a hydrocarbon (or other combines with oxygen to produce
carbon dioxide,
water
heat (flame)
The reaction of oxygen with any substance
If a combustion reaction is possible then the substance will burn
Commonly known as burning, the reaction of oxygen with any substance

67. Combustion Reactions heat heat heat Examples
The combustion reaction of hydrocarbons produces carbon dioxide, water, and heat
The combustion of propane
The combustion of glucose
The combustion of sulfur
Also a combination reaction, also produces heat
heat
hydrocarbon
heat
The combustion of sulfur also produces sulfur trioxide
hydrocarbon
heat

68. Classifying Chemical Reactions
Chemical reactions can be separated into groups of similar reactions
There are several ways to group reactions but most can be placed into one of four classes
Synthesis
Decomposition
Single-displacement
Double-displacement

69. Classifying Chemical Reactions
Synthesis Reactions
Reactions in which two or more substances combine to form a third substance
One new product forms
General form of equation:
Can have
Elements combine
An element and a compound
Two compounds
A + B AB

70. Synthesis Reactions The combinations can include Examples:
Two elements
An element and a compound
Two compounds
Examples:

71. Classifying Chemical Reactions Decomposition
Decomposition Reactions
Reactions in which one reactant breaks down into simpler (smaller) substances
Generally initiated by addition of light energy, electric current, or heating substances to high temperature
Opposite of a Synthesis Reaction
General Form of Equation AB
A + B

72. Decomposition Reactions
Can be broken down to:
Smaller compounds
Elements
Both
Examples
Symbol for heat is the delta triangle
Light is symbolized by hV

73. Classifying Chemical Reactions Single-Displacement Reactions
One element displaces another element
Forms a new compound which frees the replaced element
Most reactions occur in an aqueous solution
General Form of Equation
A + BC
AC + B

74. Single-Displacement Reactions
In this type of single-displacement reaction there are two types
Metal displaces a metal
Metal displaces hydrogen
Examples: fi
metal
displaces
metal
metal
displaces
hydrogen

75. Classifying Chemical Reactions Double-Replacement Reactions
Double-Displacement Reactions
Two compounds exchange ions or atoms to form new compounds
Also called exchange reactions
Shows the exchange of “associates” when comparing the reactants and products
General Form of Equation
AB + CD
AD + BC

76. Double Replacement Reactions
Most of these reactions occur in aqueous solution
Most involve acids, bases, and ionic compounds
Products formed
Precipitate (a solid that is insoluble)
A gas
Water

77. Double Replacement Reactions
Examples:
precipitate
gas
water

78. Summary of Reaction Types

79. End