1. CHEMICAL REACTIONS
CHAPTER 8

2. Chemical Formulas
Chemical formulas tell us how many and what kinds of atoms make up a compound
H2O has two Hydrogen atoms and one oxygen atom

3. Counting Atoms…examples
Al2O3
NH3 H2
NaCl
Na3PO4

4. Chemical reaction
During a chemical reaction, bonds between atoms a broken, rearranged and reformed
Reactants = what you start a chemical reaction with
Products = what you “produce” or end with

5. Chemical equations + C O2 CO2
Shorthand way of representing chemical reactions
Reactants and products separated by an arrow
Reactants = “yields” or produces
Reactants = left of the arrow
Products = right of the arrow
When shown pictorially, it is easy to see the the number of carbon atoms on the left hand side of the arrow are equal to the number of carbon atoms on the tight hand side of the arrow and the same thing holds true for oxygen. This equation is said to be balanced. + C O2
CO2
REACTANTS  PRODUCTS

6. Symbols Used in Chemical Equations
States of matter
(s) = solid, (l) = liquid, (g) = gas
(aq) = solution; compound dissolved in water
= gas formed (sign that a reaction has taken place)
= solid formed (also known as a precipitate)
Δ = heat

7. Law of Conservation of Matter
definition: matter cannot be created or destroyed
The number of atoms on one side of the equation have to equal the number of atoms on the other side of a chemical equations
CO2 + C O2

8. Balancing Chemical Equations
The number of atoms on one side of the equation have to equal the number of atoms on the other side of a chemical equations
H2O + CO2 +
CH4 O2
REWRITTEN AS
2H2O + CO2 +
CH4
2O2

9. Practice Balancing Equations with paperclips

10. Subscripts and Coefficients
Coefficients – balance the reaction
Subscripts - # of elements in a compound
2H2O + CO2 +
CH4
2O2

11. Subscripts and Coefficients

12. Balancing Reactions
C6H12O O2  6CO H2O

13. Balancing Reactions
C3H O2  CO H2O

14. Practice Balancing Equations worksheet

15. Balancing Reactions

16. Signs that a chemical reaction has taken place
A gas is formed
A change in color
An odor
Energy is consumed or given off (heat, light, etc.)
A new substance forms

17. Types of chemical reactions
Synthesis (Combination)
Decomposition
Single replacement
Double replacement
Combustion

18. Synthesis (Combination ; “marriage”)
Two or more reactants, one product
EX: 2Mg + O2  2MgO
EX: 2Na + Cl2  2NaCl
Magnesium and oxygen (combustion) to produce magnesium oxide…have student weight the magnesium ribbon before burning and then after burning. Mass of magnesium oxide should be more than the starting mass of magnesium because of the incorporation of oxygen.

19. Decomposition (“DIVORCE”)
One reactant, two or more products
Difficult to predict
Requires energy
EX: 2 H2O  2 H2 + O2
Decomposition of water to produce hydrogen and oxygen gas (test hydrogen gas with lit splint and oxygen gas with glowing splint)
Decomposition of baking soda to produce carbon dioxide gas (test with lit splint, should go out and then relight when exposed to oxygen)

20. 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)

21. Single Replacement (“THE AFFAIR”)
Two reactants and two products
Atoms of an element replace the atoms of a second element In a compound
Magnesium and hydrochloric acid (hydrogen produced as magnesium replaces hydrogen)
Gold (ring) and hydrochloric acid however does nothing because gold is less reactive than magnesium…one of the reasons why gold is used for jewelry.
Copper wire in silver nitrate solution (copper replaces silver, silver produced as product)

22. Single Replacement (“THE AFFAIR”)
Must consult an activity series
The element that is displaced must be less active than the element that displaces it
The more “active” element “wins”
A non-reactive metal will not replace a more reactive metal = NO REACTION TAKES PLACE

23. ACTIVITY SERIES OF METALS

24. Single Replacement (“THE AFFAIR”)
iron will replace copper
Fe + CuCl2  FeCl2 + Cu
but copper will not replace iron… Cu + FeCl2  NO RXN
Iron filings, copper chloride
Copper wire, iron chloride

25. Single Replacement (“THE AFFAIR”)
Magnesium and hydrogen
Mg + HCl 
Gold and hydrogen? Au + HCl 

26. What types of Reactions are these?
Mg + HCl→
Au + HCl→
Zn AgNO3+ →
Ag Cu(NO3)2 →

27. Double Replacement (“WIFE SWAP”)
Two reactants and two products
Signs of reaction include (one of three possibilities)
precipitate forms
gas produced
water is a product
General form:
AB + CD  AD + CB
EX: AgNO3 + HCl  HNO3 + AgCl

28. Double Replacement (“WIFE SWAP”)

29. Combustion (The Argument)
Compound and oxygen
Products are carbon dioxide and water
EX: CH4 + O2  CO2 + H2O

30. Can you name the 5 different types of reactions we learned about?
Combination (synthesis)…marriage
Decomposition …divorce
Single-replacement…the affair
Double-replacement…wife swap
Combustion…the argument

31. What types of Reactions are these?
Mg + HCl→
Au + HCl→
Zn AgNO3+ →
Ag Cu(NO3)2 →

32. Rank these metals from most reactive to least reactive
Mg, Al, Zn, Fe, Pb, Cu

33. Identify the reaction type
NaCl + H2SO4  Na2SO4 + HCl

34. Identify Reaction Type Synthesis, Decomposition, SR, DR, Combustion
NaNO3  NaNO2 + O2
CO + O2  CO2
NaCl + K2SO4  KCl + Na2SO4
KClO3  KCl + O2
CH4 + O2  CO2 + H2O
Fe + CuCl2  FeCl2 + Cu
NaCl H2SO  Na2SO4 + HCl

35. Identify Reaction Type Synthesis, Decomposition, SR, DR, Combustion
Name the reaction type…
PbO2  Pb + O2
Ca + S 
C5H12 + O2 
NaCl + K2SO4 
Ca + Fe2O3 

36. Examples…Predicting reactions
Name the reaction type…
PbO2 
Ca + S 
C5H12 + O2 
NaCl + K2SO4 
Ca + Fe2O3 