1. CHEMISTRY Matter and Change
Unit 9: Chemical Reactions

2. Section 9.1 Reactions and Equations
CHAPTER9
Table Of Contents
Section 9.1 Reactions and Equations
Section 9.2 Classifying Chemical Reactions
Section 9.3 Reactions in Aqueous Solutions

3. Reactions and Equations
SECTION9.1
Reactions and Equations
Recognize evidence of chemical change.
chemical change: a process involving one or more substances changing into a new substance
Represent chemical reactions with equations.
Balance chemical equations.
chemical reaction
reactant
product
chemical equation
coefficient
Chemical reactions are represented by balanced chemical equations.

4. Reactions and Equations
SECTION9.1
Reactions and Equations
Chemical Reactions
The process by which one or more substances are rearranged to form different substances is called a chemical reaction.

5. Reactions and Equations
SECTION9.1
Reactions and Equations
Chemical Reactions (cont.)
Evidence that a chemical reaction may have occurred:
Change in temperature
Change in color
Odor
Gas bubbles
Appearance of a solid
Light

6. Reactions and Equations
SECTION9.1
Reactions and Equations
Representing Chemical Reactions
Chemists use statements called equations to represent chemical reactions.
Reactants are the starting substances.
Products are the substances formed in the reaction.
This table summarizes the symbols used in chemical equations.

7. Reactions and Equations
SECTION9.1
Reactions and Equations
Representing Chemical Reactions (cont.)
In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) reads as “aluminum and bromine react to produce aluminum bromide”.
Skeleton equations use symbols and formulas to represent the reactants and products. Al(s) + Br2(l) → AlBr3(s)
Both word and skeleton equations lack information about how many atoms are involved in the reaction.

8. Reactions and Equations
SECTION9.1
Reactions and Equations
Representing Chemical Reactions (cont.)
A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

9. Reactions and Equations
SECTION9.1
Reactions and Equations
Balancing Chemical Equations
This figure shows the balanced equation for the reaction between aluminum and bromine.

10. Reactions and Equations
SECTION9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
A coefficient in a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products.

11. Reactions and Equations
SECTION9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
Use the scoreboard method to balance equations
Write down the number of each atom on each side of the equation
Adjust coefficients until the number of atoms is equal on both sides

12. Reactions and Equations
SECTION9.1
Reactions and Equations
Balancing Chemical Equations (cont.)
The most fundamental law in chemistry is the law of conservation of mass.
Balanced equations show this law.

13. Reactions and Equations
SECTION9.1
Reactions and Equations

14. Which of the following is NOT a chemical reaction?
SECTION9.1
Section Check
Which of the following is NOT a chemical reaction?
A. a piece of wood burning
B. a car rusting
C. an ice cube melting into water
D. red litmus paper turning blue

15. SECTION9.1
Section Check
What is the coefficient of bromine in the equation 2Al(s) + 3Br2(l) → 2AlBr3(s)?
A. 1
B. 2
C. 3
D. 6

16. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Classify chemical reactions.
metal: an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny
Identify the characteristics of different classes of chemical reactions.

17. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
synthesis reaction
combustion reaction
decomposition reaction
single-replacement reaction
double-replacement reaction
precipitate
There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions.

18. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Types of Chemical Reactions
Chemists classify reactions in order to organize the many types.
A synthesis reaction is a reaction in which two or more substances react to produce a single product.
A + B → AB

19. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Types of Chemical Reactions (cont.)
When two elements react, the reaction is always a synthesis reaction.

20. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Types of Chemical Reactions (cont.)
In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.
Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.

21. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Decomposition Reactions
A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.
Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur.
AC → A + C2

22. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Replacement Reactions
A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.
A + BX → AX + B

23. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Replacement Reactions (cont.)
A metal will not always replace a metal in a compound dissolved in water because of differing reactivities.
An activity series can be used to predict if reactions will occur.

24. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Replacement Reactions (cont.)
Halogens frequently replace other halogens in replacement reactions.
Halogens also have different reactivities and do not always replace each other.

25. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Replacement Reactions (cont.)
Double replacement reactions occur when ions exchange between two compounds.
This figure shows a generic double replacement equation.

26. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Replacement Reactions (cont.)
The solid product produced during a chemical reaction in a solution is called a precipitate.
All double replacement reactions produce either water, a precipitate, or a gas.

27. SECTION9.2

28. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions

29. Which of the following is NOT one of the four types of reactions?
SECTION9.2
Section Check
Which of the following is NOT one of the four types of reactions?
A. deconstructive
B. synthesis
C. single replacement
D. double replacement

30. The following equation is what type of reaction?
SECTION9.2
Section Check
The following equation is what type of reaction?
KCN(aq) + HBr(aq) → KBr(aq) + HCN(g)
A. deconstructive
B. synthesis
C. single replacement
D. double replacement

31. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Describe aqueous solutions.
Write complete ionic and net ionic equations for chemical reactions in aqueous solutions.
Predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas.
solution: a uniform mixture that might contain solids, liquids, or gases

32. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
aqueous solution
solute
solvent
complete ionic equation
spectator ion
net ionic equation
Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases.

33. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Aqueous Solutions
An aqueous solution contains one or more dissolved substances (called solutes) in water.
The solvent is the most plentiful substance in a solution.

34. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Aqueous Solutions (cont.)
Water is always the solvent in an aqueous solution.
There are many possible solutes—sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions.
Compounds that produce hydrogen ions in aqueous solutions are acids.

35. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Aqueous Solutions (cont.)
Ionic compounds can also be solutes in aqueous solutions.
When ionic compounds dissolve in water, their ions separate in a process called dissociation.

36. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Types of Reactions in Aqueous Solutions
When two solutions that contain ions as solutes are combined, the ions might react.
If they react, it is always a double replacement reaction.
Three products can form: precipitates, water, or gases.

37. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Types of Reactions in Aqueous Solutions (cont.)
Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide.
2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s)
Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations.
2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s)

38. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Types of Reactions in Aqueous Solutions (cont.)
Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations.
Formulas that include only the particles that participate in reactions are called net ionic equations.
2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)

39. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Types of Reactions in Aqueous Solutions (cont.)
Some reactions produce more water molecules.
No evidence of a chemical reaction is observable.
HBr(aq) + NaOH(aq) → H2O(l) + NaBr(aq)
Without spectator ions H+(aq) + OH–(aq) → H2O(l).

40. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Types of Reactions in Aqueous Solutions (cont.)
Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide.
2HI(aq) + Li2S(aq) → H2S(g) + 2LiI(aq)

41. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Types of Reactions in Aqueous Solutions (cont.)
Another example is mixing vinegar and baking soda, which produces carbon dioxide gas.
HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)
H2CO3(aq) decomposes immediately.
H2CO3(aq) → H2O(l) + CO2(g)

42. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Types of Reactions in Aqueous Solutions (cont.)
Two reactions can be combined and represented by a single chemical reaction.

43. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Types of Reactions in Aqueous Solutions (cont.)
Reaction 1
HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)
Reaction 2
H2CO3(aq) → H2O(l) + CO2(g)
Combined equation
HCl(aq) + NaHCO3(aq) + H2CO3(aq) → H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g)
Overall equation
HCl(aq) + NaHCO3(aq) → H2O(l) + CO2(g) + NaCl(aq)

44. What is the solvent in an aqueous solution?
SECTION9.3
Section Check
What is the solvent in an aqueous solution?
A. hydrogen
B. sodium ions
C. water
D. alcohol

45. SECTION9.3
Section Check
An equation that includes only the particles that participate in a reaction is called:
A. net ionic equation
B. spectator ions
C. complete ionic equation
D. reduced ionic equation

46. Reactions and Equations
SECTION9.1
Reactions and Equations
Study Guide
Key Concepts
Some physical changes are evidence that indicate a chemical reaction has occurred.
Word equations and skeleton equations provide important information about a chemical reaction.
A chemical equation gives the identities and relative amounts of the reactants and products that are involved in a chemical reaction.
Balancing an equation involves adjusting the coefficients until the number of atoms of each element is equal on both sides of the equation.

47. Classifying Chemical Reactions
SECTION9.2
Classifying Chemical Reactions
Study Guide
Key Concepts
Classifying chemical reactions makes them easier to understand, remember, and recognize.
Activity series of metals and halogens can be used to predict if single-replacement reactions will occur.

48. Reactions in Aqueous Solutions
SECTION9.3
Reactions in Aqueous Solutions
Study Guide
Key Concepts
In aqueous solutions, the solvent is always water. There are many possible solutes.
Many molecular compounds form ions when they dissolve in water. When some ionic compounds dissolve in water, their ions separate.
When two aqueous solutions that contain ions as solutes are combined, the ions might react with one another. The solvent molecules do not usually react.
Reactions that occur in aqueous solutions are double-replacement reactions.

49. CHAPTER9
Chemical Reactions
Chapter Assessment
The law of conservation of mass requires what in a chemical reaction equation?
A. both sides of the equation to contain the same substances
B. the reactants to have the same amount of molecules as the products
C. both sides to have the same amount of atoms of each element
D. the products to have fewer molecules than the reactants

50. CHAPTER9
Chemical Reactions
Chapter Assessment
A reaction that gives off heat is what type of reaction?
A. single replacement reaction
B. double replacement reaction
C. synthesis reaction
D. combustion reaction

51. CHAPTER9
Chemical Reactions
Chapter Assessment
Ions that are present in a solution and do not participate in a chemical reaction when another substance is added are called ____.
A. spectator ions
B. reactants
C. products
D. net ions

52. CHAPTER9
Chemical Reactions
Chapter Assessment
A double replacement reaction produces all of the following except ____.
A. gases
B. solids
C. light
D. water

53. Chemical Reactions What type of reaction is the following?
CHAPTER9
Chemical Reactions
Chapter Assessment
What type of reaction is the following?
2H2O(l) + energy → H2(g) + O2(g)
A. synthesis reaction
B. decomposition reaction
C. combustion reaction
D. replacement reaction

54. Chemical Reactions What type of reaction is the following?
CHAPTER9
Chemical Reactions
Chapter Assessment
What type of reaction is the following?
2H2(g) + O2(g) → 2H2O(l)
A. replacement reaction
B. synthesis
C. decomposition reaction
D. double replacement reaction

55. CHAPTER9
Chemical Reactions
Chapter Assessment
A precipitate forms in a double replacement reaction only if:
A. the reactivities of the compounds differ
B. the new compound is denser than water
C. the new compound is soluble in water
D. the new compound is not soluble in water

56. CHAPTER9
Chemical Reactions
Chapter Assessment
A ____ is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.
A. word equation
B. skeleton equation
C. chemical equation
D. balanced equation

57. Chemical Reactions Predict the type of reaction.
CHAPTER9
Chemical Reactions
Chapter Assessment
Predict the type of reaction.
LiBr2 (aq) + 2NaOH (aq) → ____
A. synthesis reaction
B. combustion reaction
C. single replacement reaction
D. double replacement reaction

58. CHAPTER9
Chemical Reactions
Chapter Assessment
Which reactions are essentially the opposite of synthesis reactions?
A. single-replacement
B. decomposition
C. combustion
D. double-replacement