The law of conservation of mass requires that both sides of a chemical reaction equation have the same number and types of atoms. This ensures that the total mass is conserved before and after the reaction. The key is that both sides must have the same number of each type of atom, not just the same substances or same number of molecules. The correct answer is C.

2. Chemical Reactions
• The process by which one or more
substances are rearranged to form different
substances is called a chemical reaction.
And rummy tummmy

3. Chemical Reactions (cont.)
• Evidence of a chemical reaction
– Change in temperature
– Change in color
– Odor, gas, or bubbles may form.

4. 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.

5. Diatomic elements
• There are 8 elements that never want to
be alone.
• They form diatomic molecules.
• H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 , and At2
• The –ogens and the –ines
• 1 + 7 pattern on the periodic table

7. 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)
• Skeleton equations lack information about
how many atoms are involved in the reaction.

8. Convert these to equations
• Solid iron (III) sulfide reacts with gaseous
hydrogen chloride to form iron (II) chloride
and hydrosulfuric acid gas.
• Nitric acid dissolved in water reacts with
solid sodium carbonate to form liquid
water and carbon dioxide gas and sodium
nitrate dissolved in water.

9. The other way
• Fe(s) + O2(g) → Fe2O3(s)
• Cu(s) + AgNO3(aq) →
Ag(s) + Cu(NO3)2(aq)

10. 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.

11. Balancing Chemical Equations
• The most fundamental law in chemistry is
the law of conservation of mass.
• Balanced equations show this law.

12. • Atoms can’t be created or destroyed
• All the atoms we start with we must end
up with
• A balanced equation has the same
number of each element on both sides of
the equation.

13. Balancing Chemical Equations
• This figure shows the balanced equation
for the reaction between aluminum and
bromine.

14. 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.

15. Rules for balancing
• 1 Write the correct formulas for all the
reactants and products
• 2 & 3 Count the number of atoms of each
type appearing on both sides
• 4 Balance the elements one at a time by
adding coefficients (the numbers in front)
• 5 Reduce if necessary
• 6 Check to make sure it is balanced.

16. Never
• Never change a subscript to balance an
equation.
• If you change the formula you are
describing a different reaction.
• H2O is a different compound than H 2O2
• Never put a coefficient in the middle of a
formula
• 2 NaCl is okay, Na2Cl is not.

17. Example
H2 + O2 → H2O
Make a table to keep track of the elements

18. Example
H2 + O2 → H2O
R P
2 H 2
2 O 1
Need twice as much O in the product

19. Example
H2 + O 2 → 2H O
2
R P
2 H 2
2 O 1
Changes the O

20. Example
H2 + O 2 → 2H O
2
R P
2 H 2
2 O 1 2
Also changes the H

21. Example
H2 + O 2 → 2H O
2
R P
2 H 2 4
2 O 1 2
Need twice as much H in the reactant

22. Example
2H +O → 2H O
2 2 2
R P
2 H 2 4
2 O 1 2
Recount

23. Example
2H +O → 2H O
2 2 2
R P
4 2 H 2 4
2 O 1 2
The equation is balanced, has the same
number of each kind of atom on both sides

24. Example
2H +O → 2H O
2 2 2
R P
4 2 H 2 4
2 O 1 2
This is the answer
Not this

25. Balancing Chemical Equations (cont.)

26. Practice
• CH4 + O2 → CO2 + H2O
• AgNO3 + Cu → Cu(NO3)2 + Ag
• Mg + N2 → Mg3N2
• P + O2 → P4O10
• Na + H2O → H2 + NaOH

27. Section 9.1 Assessment
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 A. A
D. red litmus paper turning blue B. B
C. C
0% 0% 0% 0%
D. D
A
B
D
C

28. Section 9.1 Assessment
What is the coefficient of bromine in the
equation 2Al(s) + 3Br2(l) → 2AlBr3(s)?
A. 1
B. 2
C. 3 A. A
D. 6 B. B
C. C
0% 0% 0% 0%
D. D
A
B
D
C

29. Types of Chemical Reactions
• Chemists classify reactions in order to
organize the many types
• We will learn 5 types.
• Will be able to predict the products.
• For some we will be able to predict
whether they will happen at all.
• Will recognize them by the reactants

30. Types of Chemical Reactions (cont.)
• A synthesis reaction is a reaction in which
two or more substances combine to produce
a single product.
• When two elements react, the reaction is
always a synthesis reaction.

31. Types of Chemical Reactions (cont.)
• Predicting products of a synthesis
reaction:
• Element + Element  compound
• Fe + O2  Fe2O3 (you would be told iron (III))
– Rules of forming compounds must be
followed
• Predict the products
– Calcium reacts with chlorine
– Aluminum reacts with oxygen

32. 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.

33. Two specific types of combustion
•If compound composed of only C, H and
maybe O is reacted with oxygen, there are
two possible outcomes
•Complete combustion will produce CO 2 and
H2O.
•Incomplete combustion will produce CO
and H2O.

34. Predict Products of combustion reactions:
•C4H10 + O2 → (complete)
•C4H10 + O2 → (incomplete)
•C6H12O6 + O2 → (complete)
•C8H8 + O2 → (incomplete)
•Mg + O2 

35. 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.
• Compound  Element or compound +
Element or compound

36. • Predicting Products of Decomposition
• Easily predict the products if it is a binary
compound
• Made up of only two elements
• Compound will fall apart into its elements
• H2O   → 
electricity
electricity
  →
• HgO
→ heat

37. 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

38. • We can tell whether a reaction will
happen
• Some elements are more reactive than
others
• Use Activity Series List
• More reactive replaces less reactive
– Higher on the list replaces lower.
– If the element by itself is higher, reaction
occurs, if lower it doesn’t

39. Replacement Reactions (cont.)

40. • Fe + CuSO4 →
• Pb + KCl →
• Al + HCl →
• What does it mean that Ag, Pt and Au are
on the bottom of the Activity Series List?

41. Replacement Reactions (cont.)
• Halogens frequently replace other
halogens in replacement reactions.
• Halogens also have different reactivities and
do not always replace each other.

42. • The order of activity is on the periodic
table.
• Higher replaces lower.
• F2 + HCl →
• Br2 + KCl →

43. Replacement Reactions (cont.)
• Double replacement reactions occur
when ions exchange between two
compounds.
• This figure shows a generic double
replacement equation.

44. Replacement Reactions (cont.)
• A 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.

45. Complete and Balance
•assume all of the reactions take place.
•CaCl2 + NaOH →
•CuCl2 + K2S →
•KOH + Fe(NO3)3 →
•(NH4)2SO4 + BaF2 →

46. Replacement Reactions (cont.)
• This table summarizes different ways to
predict the products of a chemical reaction.

47. Examples
• H2 + O2 →
• H2O →
• Zn + H2SO4 →
• HgO →
• KBr +Cl2 →
• AgNO3 + NaCl →
• Mg(OH)2 + H2SO3 →

48. Section 9.2 Assessment
Which of the following is NOT one of the
four types of reactions?
A. deconstructive
B. synthesis
C. single replacement A. A
D. double replacement B. B
C. C
0% 0% 0% 0%
D. D
A
B
D
C

49. Section 9.2 Assessment
The following equation is what type of
reaction?
KCN(aq) + HBr(aq) → KBr(aq) + HCN(g)
A. deconstructive
B. synthesis A. A
C. single replacement B. B
D. double replacement C. C
0% 0% 0% 0%
D. D
A
B
D
C

50. 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.

51. 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.

52. 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.

53. 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.

54. 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)

55. 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)

56. 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).

57. 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)

58. Section 9.3 Assessment
What is the solvent in an aqueous
solution?
A. hydrogen
B. sodium ions
C. water A. A
D. alcohol B. B
C. C
0% 0% 0% 0%
D. D
A
B
D
C

59. Section 9.3 Assessment
An equation that includes only the
particles that participate in a reaction is
called:
A. net ionic equation
B. spectator ions
A. A
C. complete ionic equation B. B
D. reduced ionic equation C. C
0% 0% 0% 0%
D. D
A
B
D
C

60. Section 9.1 Reactions and Equations
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.

61. Section 9.2 Classifying Chemical
Reactions
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.

62. Section 9.3 Reactions in
Aqueous Solutions
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.

63. 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
A. A
C. both sides to have the same amount
of atoms of each element B. B
D. the products to have fewer molecules C. C
than the reactants 0% 0% 0% 0%
D. D
A
B
C
D

64. A reaction that gives off heat is what type
of reaction?
A. single replacement reaction
B. double replacement reaction
C. synthesis reaction A. A
D. combustion reaction B. B
C. C
0% 0% 0% 0%
D. D
A
B
D
C

65. 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 A. A
B. B
C. products
C. C
D. net ions 0% 0% 0% 0%
D. D
A
B
D
C

66. A double replacement reaction produces
all of the following except ____.
A. gases
B. solids
C. light A. A
D. water B. B
C. C
0% 0% 0% 0%
D. D
A
B
D
C

67. What type of reaction is the following?
2H2O(l) + energy → H2(g) + O2(g)
A. synthesis reaction
B. decomposition reaction
A. A
C. combustion reaction
B. B
D. replacement reaction C. C
0% 0% 0% 0%
D. D
A
B
D
C

68. What type of reaction is the following?
2H2(g) + O2(g) → 2H2O(l)
A. replacement reaction
B. synthesis
A. A
C. combustion reaction
B. B
D. double replacement reaction C. C
0% 0% 0% 0%
D. D
A
B
D
C

69. 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 A. A
B. B
C. the new compound is soluble
in water C. C
0% 0% 0% 0%
D. the new compound is not D. D
A
B
D
C
soluble in water

70. 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 A. A
B. B
C. chemical equation
C. C
D. balanced equation 0% 0% 0% 0%
D. D
A
B
D
C

71. Predict the type of reaction.
LiBr2 (aq) + 2NaOH (aq) → ____
A. synthesis reaction
B. combustion reaction
A. A
C. single replacement reaction
B. B
D. double replacement reaction C. C
0% 0% 0% 0%
D. D
A
B
D
C

72. Which reactions are essentially the
opposite of synthesis reactions?
A. single-replacement
B. decomposition
C. combustion A. A
D. double-replacement B. B
C. C
0% 0% 0% 0%
D. D
A
B
D
C