1. CHEMICAL REACTIONS
CHAPTER 8

2. DESCRIBING CHEMICAL CHANGE
8.1

3. Chemical Reaction REACTANTS  PRODUCTS
One or more substances change into one or more new substances
Reactants = substances that are reacting or changing
Products =substances being formed from the reactants
REACTANTS  PRODUCTS

4. Chemical Equations REACTANTS  PRODUCTS
Describe chemical reactions using words instead of symbols
The  means “yields” or “reacts to produce”
REACTANTS  PRODUCTS

5. Symbols Used in Chemical Equations
Symbols used to show state of matter
l=liquid (only water), s=solid, g=gas
Other symbols used
aq = aqueous solution = made with water
 or heat = written over the  to show heat was added

6. Catalysts and Chemical Reactions
Catalyst = A substance that speeds up the rate of a reaction
NOT a reactant or a product
NOT used up in a reaction
If present, the name of the catalyst will be written over the  in a chemical equations
Ex: MnO2, Pt, heat, 

7. Skeleton Equations Do not indicate relative amounts
Show just the formulas of the reactants and the products
unbalanced

8. Chemical Equation Example #1
Iron reacts with oxygen to produce iron (III) oxide
Translates into…
Iron + oxygen  Iron (III) oxide

9. Back to Chemical Equation Example #1
Iron reacts with oxygen to produce iron (III) oxide
Translates into…
Iron + oxygen  Iron (III) oxide
Fe (s) + O2 (g) Fe2O3 (s)

10. Chemical Equation Example #2
Hydrogen peroxide reacts to produce water and oxygen gas
Translates into…
Hydrogen peroxide  water + oxygen

11. Skeleton Equation Example #2
Hydrogen peroxide reacts to produce water and oxygen gas
Translates into…
Hydrogen peroxide  water + oxygen
H2O2 (l)  H2O (l) + O2 (g)

12. Chemical Equation Example #3
Carbon tetrahydride (methane) burns in the presence of oxygen gas to produce carbon dioxide and water
Translates into…
Methane + oxygen  carbon dioxide + water

13. Back to Chemical Equation Example #3
Gaseous Carbon tetrahydride (methane) burns in the presence of oxygen gas to produce carbon dioxide and water
Translates into…
Methane + oxygen  carbon dioxide + water
CH4 (g) + O2 (g)  CO2 (g) + H2O (g)

14. Your turn…write a skeleton equation
Sulfur burns in the presence of oxygen to form sulfur dioxide
Heating potassium chlorate in the presence of the catalyst manganese (IV) oxide produces oxygen gas and solid potassium chloride

15. 1. S (s) + O2 (g)  SO2 (g) MnO2, Δ 2. KClO3 (s)  O2 (g) + KCl (s)
Check your Answers…
1. S (s) + O2 (g)  SO2 (g) MnO2, Δ 2. KClO3 (s)  O2 (g) + KCl (s)

16. Your turn…write a sentence
3. KOH (aq) + H2SO4 (aq)  H2O (l) + K2SO4 (aq)
4. Na (s) + H2O (l)  NaOH (aq) + H2 (g)

17. Check your Answers…
3. aqueous potassium hydroxide and aqueous sulfuric acid produces water and aqueous potassium sulfate 4. solid sodium is added to water. Hydrogen gas and aqueous sodium hydroxide are produced

18. Balancing Chemical Equations (1)
Law of Conservation of Matter
Matter cannot be created nor destroyed but only rearranged
The number of atoms on each side of the equation must be equal
How many Hydrogen atoms?
How many oxygen atoms?
How many Hydrogen atoms?
How many oxygen atoms?
2 H
2 O
2 H
1 O

19. Balancing Chemical Equations (2)
A balanced equation has the same # of atoms of each element on each side of the equation
Coefficients are numbers placed in front of the symbols for reactants and products to balance

20. Balancing Chemical Equations (3)
C (s) + O2 (g)  CO2 (g)
C (s) + O2 (g)  CO (g)
This equation is balanced because each side of the equation has the same # of carbon and oxygen atoms
This equation is NOT balanced because each side of the equation has different # of oxygen atoms

21. Rules for Balancing Chemical Equations
Determine correct formulas for all the reactants and products
Write the skeleton formula
Count the # of each element on each side of the equation (atomic inventory)
NEVER CHANGE A SUBSCRIPT!!

22. Rules for Balancing Chemical Equations
Recheck atomic inventory
Make sure the coefficients are in the lowest whole number ratio

23. Helpful Hints for Balancing Equations
POLYATOMICS: treat polyatomic ions as units if present on both sides
DIATOMICS: remember seven at seven?
can have ½ as a coefficient

24. Example #1 And the answer… H2 (g) + O2 (g)  H2O (l)

25. 2 NaCl (s) + H2SO4 (aq)  Na2SO4 (s) + 2 HCl (aq)
Example #2
NaCl (s) + H2SO4 (aq)  Na2SO4 (s) + HCl (aq)
And the answer…
2 NaCl (s) + H2SO4 (aq)  Na2SO4 (s) + 2 HCl (aq)

26. And the answer… Fe (s) + O2 (g)  Fe2O3 (s)
Example #3
Fe (s) + O2 (g)  Fe2O3 (s)
4 Fe (s) + 3 O2 (g)  2 Fe2O3 (s)
And the answer…

27. Practice in Packet…page 13 – finish for homework
YOUR TURN…
Practice in Packet…page 13 – finish for homework
Balancing Equations

28. Types of Reactions
8.2
8.3
Predicting Reactions

29. Combination (synthesis) Decomposition Single-replacement
Types of reactions
Combination (synthesis)
Decomposition
Single-replacement
Double-replacement
Combustion
Oxidation/reduction (LATER)
Acid/Base (LATER)

30. 1. Combination reactions (synthesis) general
Two or more substances react to form a single substance
Reactants are normally 2 elements
General equation: (marriage)
A + B  AB

31. 1. Combination reactions (synthesis) EXAMPLES
4Al + 3O2  2Al2O3
3Mg + N2  Mg3N2

32. If you see two elements A + B 
1. Combination reactions (synthesis) predicting products
If you see two elements A + B 
Determine charges of each atom (review ion sheet)
Form a neutrally balanced product
Balance equation

33. 2. Decomposition reactions (divorce) general
single compound broken down into two or more elements or compounds
Difficult to predict
Requires energy (heat, light, electricity)
General equation: (divorce)
AB  A + B

34. 2. DEComposition reactions EXAMPLES
2H20(l)  2H2(g) + O2(g)
2 HgO (s)  2 Hg (l) + O2 (g)
electricity

35. If you see one compound AB 
2. DEComposition reactions predicting products
If you see one compound AB 
Break compound into component elements
Be mindful of diatomic elements
Balance equation
Look for presence of heat () or electrolysis
Practice…Page 18 in packet

36. Practice

37. Identify… synthesis or decomposition?
NaNO3  NaNO2 + O2
CO + O2  CO2
Al + S  Al2S3
KClO3  KCl + O2
Fe + O2  Fe2O3
HgO  Hg O2
decomposition
Synthesis (combination)
Jump in packet notes to page 7

38. 3. single-replacement (the other woman/man) general
Atoms of an element replace the atoms of a second element in a compound
Two reactants and two products
Two types
Metal replacing metal
A + BC  AC + B
Nonmetal replacing nonmetal
A + BC  BA + C

39. 3. single-replacement METAl replacing metal
The element that is displaced must be less active than the element that displaces it
Activity Series of metals: lists metals in order of decreasing reactivity
A non-reactive metal will not replace a more reactive metal = NO REACTION

40. ACTIVITY SERIES OF METALS

41. 3. single-replacement EXAMPLES – metal replacing metal
iron will replace copper
Fe + CuCl2  FeCl2 + Cu
Fe2+ Cu2+ Cl-
but copper will not replace iron… Cu + FeCl2  NO RXN

42. 3. single-replacement nonmetal replacing nonmetal
Nonmetals can only replace nonmetals (second substance in the compound)
Limited to the halogens
Activity decreases as you go down group 17 on periodic table

43. 3. single-replacement EXAMPLES – nonmetal replacing nonmetal
Cl2 + 2 NaBr  2 NaCl + Br2
Cl Na+ Br- (Cl more active than Br)
I2 + NaBr  NO RXN
I Na+ Br (Br more active than I)

44. Will the single replacement reaction occur?
Mg(s) + 2 HCl(aq) →
Br2 + 2KI →
2AgNO3(aq) + Zn(s) →
Ag + Cu(NO3)2 →
Cl2 + 2NaBr →
Au + HCl →
I2 + 2KBr →
Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
Br2 + 2KI → 2KBr + I2
2AgNO3(aq) + Zn(s) → 2Ag(s) + Zn(NO3)2(aq)
Ag + Cu(NO3)2 → No reaction
Cl2 + 2NaBr → 2NaCl + Br2
Au + HCl → No reaction
I2 + 2KBr → no reaction
Predicting…go to page 7 in notes

45. Predicting single replacement
Read Only
Predicting single replacement
If you see one element and one compound A + BC 
Identify ions of each atom
Determine what can replace what (cation- to-cation or anion-to-anion)
Be mindful of diatomic elements
Consult activity series chart
Make neutral compound and atom
Balance equation!!!
Practice in packet…page 19

46. 4. Double replacement (wife swap) General
Exchange of positive ions between ionic compounds in solution
General equation: (wife swap)
AB + CD  AD + CB

47. 4. Double replacement (wife swap)
Solubility table: table that shows solubility of two ions
Where they intersect is either:
S=soluble  meaning an aqueous substance is formed and a (aq) follows the formula
I=insoluble  meaning ppt is formed and a ↓follows the formula

48. Solubility table

49. 4. Double replacement (wife swap)
Solubility rules:
All nitrates are soluble
All potassium compounds are soluble
Others are on solubility chart in packet
If there is no ppt, gas or water made and only aqueous substances – NO RXN
AgNO3 (aq) + KCl (aq)  AgCl (aq) + KNO3 (aq)
NO RXN!

50. 4. Double replacement (wife swap) examples
2 NaOH (aq) + H2SO4 (aq)  Na2SO4 (aq) + 2 H2O (l) Driving force is the formation of water
BaCl2 (aq) + K2CO3 (aq)  BaCO3  + 2 KCl (aq) Driving force is the formation of a precipitate
FeS (s) HCl (aq)  H2S  + FeCl2 (aq) Driving force is the formation of a gas

51. Predicting double replacement
Read Only
Predicting double replacement
If you see two compounds AB + CD 
Identify ions of each atom
Switch the cations by bonding the outside ions together and the inside ions together
Make new neutral compounds
Consult solubility table and match up new ion pairs
S=soluble (place an (aq) after the compound)
I=insoluble (place a  after the compound)
Balance the equation

52. 4. Combustion reactions General Info
An element or compound reacts with oxygen
Produces heat and light
Combustion of an element produces the element oxide
A + O2  AO
Combustion of a hydrocarbon ALWAYS produces carbon dioxide and water
CxHy + O2  CO2 + H2O

53. 4. Combustion reactions EXAMPLES
Benzene:
C6H6 (l) O2  6 CO H2O
Methyl alcohol:
CH3OH (l) O2  CO2 + 2 H2O
Magnesium:
2Mg + O2  2MgO

54. Predicting combustion
Read Only
Predicting combustion
If you see two hydrocarbon and oxygen CxHy + O2 
Products are always CO2 and H2O
Balance the equation
If you see an element and oxygen
A+ O2 
Combustion and/or combination
Follow steps for combination

55. Types of reactions…summary
Combination (synthesis)…marriage
Decomposition …divorce
Single-replacement…the other man
Double-replacement…wife swap
Combustion…the argument
Oxidation/reduction (LATER)
Acid/Base (LATER)

56. Examples… Predicting reactions
Write the following examples in your notes
1. PbO2 
2. Ca + S 
3. C5H12 + O2 
4. NaCl + K2SO4 
5. Ca + Fe2O3 

57. Examples… Predicting reactions
Describe the reactants…
1. PbO2  1 compound
2. Ca + S  2 elements
3. C5H12 + O2  hyrdrocarbon & O2
4. NaCl + K2SO4  2 compounds
5. Ca + Fe2O3  1 element & 1 compound

58. Examples… Predicting reactions
Name the reaction type…
1. PbO2  decomposition divorce
2. Ca + S  synthesis marriage
3. C5H12 + O2  combustion argument
4. NaCl + K2SO4  double replace. wife swap
5. Ca + Fe2O3  single replace. the other man

59. Examples… Predicting reactions
Predict the products and balance….
1. PbO2  Pb (s) + O2 (g)
2. Ca + S  CaS
3. C5H12 + 8O2  5CO2 + 6H2O (balance!)
4. NaCl + K2SO4  Na2SO4 (aq) + KCl (aq)
NO RXN! = BOTH (aq)
5. 3Ca + Fe2O3  3CaO + 2Fe (s)

60. COMPLETE IONIC EQUATIONS
8.4

61. Things to remember…double replacement
Two ionic compounds react by exchanging cations
AB + CD → AD + CB
AgNO3 + NaCl → AgCl + NaNO3
One of the products must be:
A gas
Water
A precipitate (solid)

62. Aqueous solutions Many important reactions take place in water
Ionic compounds dissociate in aqueous solutions
Therefore, they are written as aqueous ions
AgNO3 (aq) = Ag+ (aq) + NO3- (aq)

63. COMPLETE IONIC EQUATION
An equation that shows ionic compounds as their free ions
EX: AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
Reactants really exist as and are written as:
Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq) …
Only aqueous products are written as ions:
 AgCl (s) + Na+ (aq) + NO3- (aq)

64. Spectator ions Spectator Ions = Na+ (aq) + NO3- (aq)
Ions that appear on both sides do NOTHING in the reaction and are referred to as spectator ions:
Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq) …
AgCl (s) + Na+ (aq) + NO3- (aq)
Spectator Ions = Na+ (aq) + NO3- (aq)

65. Net ionic equations Net ionic equation: Ag+ (aq) + Cl- (aq)  AgCl (s)
Spectator ions can be omitted from both sides of the original equation
Shows the particles that actually take part in the reactions
Spectator ions = Na+ (aq) and NO3-(aq)
Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq) …
AgCl (s) + Na+ (aq) + NO3- (aq)
Net ionic equation: Ag+ (aq) + Cl- (aq)  AgCl (s)

66. Practice
Write the complete ionic equation and net ionic equation for the following reactions. Identify Spectator ions as well. BALANCE!!!
EX: aqueous calcium hydroxide reacts with aqueous phosphoric acid