1. Ch. 8 – Chemical Reactions
Intro to Reactions

2. Signs of a Chemical Reaction
Evolution of heat and light
Formation of a gas
Formation of a precipitate
Color change

3. Law of Conservation of Mass
mass is neither created nor destroyed in a chemical reaction
total mass stays the same
atoms can only rearrange
4 H
2 O
4 H
2 O
36 g
4 g
32 g

4. Chemical Equations
A+B  C+D
REACTANTS
PRODUCTS

5. Symbols used in Equations

6. 2H2(g) + O2(g)  2H2O(g) Writing Equations
Identify the substances involved.
Use symbols to show:
How many? - coefficient
Of what? - chemical formula
In what state? - physical state
Remember the diatomic elements.

7. Writing Equations 2 Al (s) + 3 CuCl2 (aq)  3 Cu (s) + 2 AlCl3 (aq)
Two atoms of solid aluminum react with three units of aqueous copper(II) chloride to produce three atoms of solid copper and two units of aqueous aluminum chloride.
How many?
Of what?
In what state? 2 Al
(s)
+ 3
CuCl2
(aq)
 3 Cu
(s)
+ 2
AlCl3
(aq)

8. Describing Equations Describing Coefficients: individual atom = “atom”
covalent substance = “molecule”
ionic substance = “formula unit”
3 molecules of carbon dioxide
2 atoms of magnesium
4 formula units of magnesium oxide
3CO2 
2Mg 
4MgO 

9. Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
Describing Equations
Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
How many?
Of what?
In what state?
One atom of solid zinc
reacts with
two molecules of aqueous hydrochloric acid
to produce
one unit
of aqueous zinc chloride
and one
molecule of hydrogen gas.

10. Ch. 8 – Chemical Reactions
Balancing Equations

11. Coefficient  subscript = # of atoms
Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Coefficient  subscript = # of atoms
4. Reduce coefficients to lowest possible ratio, if necessary.
5. Double check atom balance!!!

12. Helpful Tips Balance one element at a time.
If Hydrogen and Oxygen appear, balance them last. Balance Hydrogen before Oxygen.
Update ALL atom counts after adding a coefficient.
If an element appears more than once per side, balance it last.

13. Balancing Example 2 Al + CuCl2  Cu + AlCl3 Al Cu Cl 3 3 2 2  1 1 2 3
Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2
Al CuCl2  Cu AlCl3 Al Cu Cl 3 3 2
2 
 2
 6
3 
6 
 3

14. Balancing Example
Aqueous nitric acid reacts with solid magnesium hydroxide to produce aqueous magnesium nitrate and water
(2,1,1,2)
Solid Calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas.
(1,2,1,1)

15. Balancing example (hydrocarbons)
Ethane gas reacts with oxygen gas to form carbon dioxide and water.
Ethene gas reacts with oxygen gas to form carbon dioxide and water.
Butane gas reacts with oxygen gas to form carbon dioxide and water.

16. Types of Chemical Reactions
Ch. 8 – Chemical Reactions
Types of Chemical Reactions

17. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Combustion
the burning of a hydrocarbon in O2 to produce heat
A + O2  B
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

18. Combustion C3H8(g)+ O2(g)  5 3 4 CO2(g)+ H2O(g) Products:
form CO2 + H2O
Form carbon monoxide and/or carbon if there is limited oxygen
C3H8(g)+ O2(g) 
CO2(g)+ H2O(g)

19. Synthesis (Combination)
the combination of 2 or more substances to form a compound
only one product
A + B  AB

20. Synthesis (Combination)
H2(g) + Cl2(g)  2 HCl(g)

21. Synthesis (Combination)
Products:
If products are ionic - cancel charges
If covalent - hard to tell
Al(s)+ Cl2(g) 
AlCl3(s)

22. Decomposition
a compound breaks down into 2 or more simpler substances
only one reactant
AB  A + B

23. Decomposition
2 H2O(l)  2 H2(g) + O2(g)

24. Decomposition 2 2 KBr(l)  K(s) + Br2(l) Products:
binary - break into elements
others - hard to tell (more on this later)
KBr(l) 
K(s) + Br2(l)

25. Synthesis Reactions to know
Almost all metals react with oxygen to form metal oxides.
Ex/ Magnesium reacts with oxygen to form Magnesium oxide

26. Synthesis reactions to know
Nonmetals also form oxides.
Sulfur reacts with oxygen to form Sulfur dioxide
Carbon reacts with oxygen to form Carbon dioxide

27. Synthesis reactions involving water to know
Oxides of active metals react with water to produce metal hydroxides.
Ex/ Calcium oxide reacts with water to form calcium hydroxide.

28. Synthesis reactions to know involving water
Many oxides of nonmetals in the upper right portion of the periodic table react with water to produce oxyacids (acids with oxygen).
Ex/ sulfur dioxide reacts with water to form sulfurous acid

29. Decomposition reactions to know
Metal carbonates break down to produce a metal oxide and carbon dioxide gas.
Ex/ calcium carbonate decomposes to produce calcium oxide and carbon dioxide.

30. Decomposition reactions to know
All metal hydroxides except those containing group 1 metals decompose when heated to yield metal oxides and water.
Ex/ calcium hydroxide decomposes to produce calcium oxide and water.
End 6th

31. Decomposition reactions to know
Metal chlorates decompose to produce a metal chloride and oxygen.
Ex/ potassium chlorate decomposes in the presence of the catalyst Manganese dioxide to produce potassium chloride and oxygen.
End pd 3

32. Decomposition reactions to know
Sulfites decompose into the cation oxide and sulfur dioxide gas
Calcium sulfite decomposes to form calcium oxide and sulfur dioxide gas.

33. Decomposition reactions to know
Peroxides decompose into the oxide of the cation and oxygen gas.
Hydrogen peroxide decomposes to form water (dihydrogen monoxide) and oxygen gas.
Sodium peroxide decomposes to form . . .

34. Decomposition reactions to know
Certain acids decompose into nonmetal oxides and water.
Ex/ Carbonic acid is unstable and decomposes readily to produce carbon dioxide and water.
Sulfurous acid decomposes to produce sulfur dioxide and water.
Ended 1st

35. Decomposition reactions to know
Ammonium salts decompose into ammonia and the acid of the anion.
Ex/ Ammonium acetate decomposes to form ammonia and acetic acid.
Ammonium nitrate decomposes to form ammonia and nitric acid.

36. A + BC  B + AC Single Replacement
one element replaces another in a compound
metal replaces metal (+)
nonmetal replaces nonmetal (-)
A + BC  B + AC

37. Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Single Replacement
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

38. Single Replacement Fe(s)+ CuSO4(aq)  Cu(s)+ FeSO4(aq)
Products:
Metal atom  metal cation(+)
Nonmetal atom  nonmetal anion(-)
free element must be more active (check activity series)
Fe(s)+ CuSO4(aq) 
Cu(s)+ FeSO4(aq)
Br2(l)+ NaCl(aq) 
N.R.

39. AB + CD  AD + CB Double Replacement
Occurs between two aqueous ionic compounds
ions in two compounds “change partners”
cation of one compound combines with anion of the other
AB + CD  AD + CB

40. Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)
Double Replacement
Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)

41. Double Replacement Pb(NO3)2(aq)+ KI(aq)  2 2 PbI2(s)+ KNO3(aq)
Products:
In order for a reaction to occur one of the following must occur
one product must be insoluble (a precipitate) (check solubility table)
A gas is produced
A covalent compound (molecular) is produced
Pb(NO3)2(aq)+ KI(aq) 
PbI2(s)+ KNO3(aq)
NaNO3(aq)+ KI(aq) 
N.R.

42. Examples Solutions of Hydrochloric acid and Sodium hydroxide are mixed
Solutions Rubidium carbonate and acetic acid are mixed

43. Writing net ionic equations
1. Write the skeleton equation
Make sure charges ions are balanced.
2. Write the total ionic equation
3. Cancel out ions that appear on both sides
4. These are called spectator ions.
Spectator ions do not take part in the overall net reaction.

44. Writing net ionic equations
A solution of Lead (II) nitrate is mixed with a solution of potassium iodide.
A solution of silver nitrate is mixed with a solution of sodium hydroxide.
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45. Predicting products from reactions
If given only reactants
Figure out what type of reaction it is
Write the products. If one of the products is ionic, balance charges.
Balance the equation
Ex/ Hydrochloric acid is mixed with zinc metal.

46. Predicting (cont’d) Calcium metal burns in the presence of oxygen.
Sodium carbonate is heated vigorously.
Potassium chlorate is heated vigorously.
Pentane burns in oxygen.
Aqueous silver nitrate is mixed with aqueous sodium chloride.

47. Predicting products Hydrochloric acid is mixed with Sodium hydroxide.
Gold metal is dropped into hydrochloric acid.