1. Ch. 8 – Chemical Reactions
Intro to Reactions

2. Describing a Chemical Reaction
A Chemical Reaction is the process by which one or more substances are changed into one or more different substances.
It is represented by a Chemical Equation.

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

4. Signs of a Chemical Reaction
Evolution of heat and light
Formation of a gas
Formation of a precipitate (i.e. solid)
Color change

5. Law of Conservation of Mass
Mass is neither created nor destroyed in a chemical reaction, simply rearranged.
Total mass stays the same
Total # atoms stay the same
4 H
2 O
4 H
2 O
36 g
4 g
32 g

6. 2H2(g) + O2(g)  2H2O(g) Writing Equations
Identify the substances involved
Answer the following questions:
How many? – coefficient
Of what? – chemical formula
In what state? – (s), (l), (g), (aq)

7. “ #7 makes a 7…and don’t forget Hydrogen” - (makes 7 total)
Diatomic Elements
Hydrogen
Nitrogen
Oxygen
Flourine
Chlorine
Bromine
Iodine
“ #7 makes a 7…and don’t forget Hydrogen” - (makes 7 total) or
“HOFBrINCl”

8. Symbols used in Equations
Meaning 
“Yields”
(s)
Solid
(l)
Liquid
(g)
Gas
(aq)
Aqueous (solid dissolved in water)
Reactants are heated

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. 2Al(s) + 3CuCl2(aq)  3Cu(s) + 2AlCl3(aq)
Writing Equations
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.
What?
How many?
In what state?
2Al(s) + 3CuCl2(aq)  3Cu(s) + 2AlCl3(aq)

11. Ch. 8 – Chemical Reactions
Balancing Equations

12. Balancing

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

15. Helpful Tips Balance one element at a time
Leave Hydrogen and Oxygen for last
Update ALL atom counts after adding a coefficient
Balance polyatomic ions as a single unit
Go to Virtual balancing examples…

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

17. Types of Reactions Synthesis reactions Decomposition reactions
Single displacement reactions
Double displacement reactions
Combustion reactions
You need to be able to identify each type.

18. Types of Reactions A + B → AB AB → A + B AB + C → AC + B
Synthesis
Decomposition
Single Replacement
Double Replacement
Combustion
A + B → AB
Two or more substances combine to form a new substance
A single compound breaks down
into two or more simpler substances
AB → A + B
AB + C → AC + B
One element replaces another element in a compound
The atoms in two different compounds trade places
AB + CD → AC + BD
A substance combines with oxygen to yield carbon dioxide and water
X + O2  CO2 + H2O

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. Practice MgF2(s) AlF3(s) Predict the products… Na(s) + Cl2(g)
Mg(s) + F2(g) 
Al(s) + F2(g) 
NaCl(s) 2 2
MgF2(s) 2 3 2
AlF3(s)
Now, balance them…

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. A + BC  B + AC Single Replacement
One element replaces a similar element in a compound
Metal (+) replaces metal (+)
Nonmetal (-) replaces nonmetal (-)
Free element must be more active (check activity series)
A + BC  B + AC

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

27. Single Replacement Products: ion + compound
Metal atom  metal cation(+)
Nonmetal atom  nonmetal anion(-)
Ni (s) + CuCl2 (aq)  NiCl2 (aq) + Cu (s)
2Al (s) + 3Pb(NO3)2 (aq)  3Pb (s) + 2Al(NO3)3 (aq)
Mg (s) + 2HCl (aq)  H2 (g) + MgCl2 (aq)
Br2 (l) + KCl (aq)  no reaction
Co (s) + 2NaCl (aq)  no reaction

28. Single Replacement Reactions
Write and balance the following single replacement reaction equation:
Zn(s) HCl(aq)  2
ZnCl2 + H2 (g) 2 2
NaF(s) Cl2 (g)
NaCl(s) F2(g) 
Al (s) Cu(NO3)2 (aq)  2 3 3
Cu (s) + Al(NO3)3 (aq) 2

29. AB + CD  AD + CB Double Displacement
The ions of two compounds change places in a aqueous solution.
ions in two compounds “change partners”
cation of one compound combines with anion of the other
AB + CD  AD + CB

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

31. Double Displacement Products:
Dbl. Displacement reaction will always produce one of the following:
A precipitate check solubility table,
2KI (aq) + Pb(NO3)2 (aq)  Pbl2 (s) + 2KNO3 (aq)
An insoluble gas that bubbles out of solution, or
FeS (s) + 2HCl (aq)  H2S (g) + FeCl2 (aq)
A soluble molecular compound that remains dissolved in the solution.
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O(l)

32. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Combustion
A substance reacts with O2, releasing heat and light
A hydrocarbon reacts with O2, producing CO2 & H2O
A + O2  B
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

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

34. Identifying Chemical Reactions
Use the codes below to classify each reaction
S = Synthesis D = Decomposition SR = Single Replacement DR = Double Replacement
____ P + O2 → P4O10 ____ Mg + O2 → MgO ____ HgO → Hg + O2 ____ Al2O3 → Al + O2 ____ Cl2 + NaBr → NaCl + Br2 ____ H2 + N2 → NH3 ____ Na + Br2 → NaBr
____ S8 + F2 → SF6
____ CuCl2 + H2S → CuS + HCl
____ C H2 → CH4
____ HgO Cl2 → HgCl O2
____ KClO3  → KCl  +  O2  
____ BaCl2  +   Na2SO4 →  NaCl   +  BaSO4

35. 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

36. Activity Series of the Elements
Ch. 8 – Chemical Reactions
Activity Series of the Elements

37. Activity Series
An activity series is a list that organizes elements according to the ease with which they react.
They are used to help predict whether a reaction will occur.
A more active element will replace a less active element in single-displacement reactions. If this is not the case, then no reaction occurs.
An element may replace any element below it, but not above it.
Do all reactions occur?
How do you know when a reaction occurs and when it does not?

38. Activity Series Do all reactions occur?
How do you know when a reaction occurs and when it does not?

39. Practice…
Will the following reactions occur? If yes, what are the products? If no, write “no reaction”
MgCl2 (aq) + Zn (s) no reaction
Al (s) + H2O (g)  Al2O3 + H2
Cd (s) + O2 (g)  CdO (s)
Br2 (l) + KCl (aq)  no reaction