1. Chapter 8-Chemical Equations & Reactions
8.1-Describing Chemical Reactions
8.2-Types of Chemical Reactions
8.3-Activity Series of the Elements

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

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

4. Chemical Equations check table p.266

5. Word vs. Formula/Chemical Eqns.
Word equations are equations in which the reactants & products are represented by words.
Methane + oxygen  carbon dioxide + water
Formula equations are equations in which the reactants & products are represented by their symbols or formulas.
CH4(g) + O2(g)  CO2(g) + H2O(g)

6. Diatomic Elements Exist as two atoms bonded together.
Remember brinclhof!
Bromine
Iodine
Nitrogen
Chlorine
Hydrogen
Oxygen
Fluorine

7. Writing Word & Formula Eqns.
Solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper(II) nitrate.
Copper + silver nitrate  silver + copper(II) nitrate
Cu(s) + AgNO3(aq)  Ag(s) + Cu(NO3)2(aq)
Solid zinc metal reacts with aqueous copper(II) sulfate to produce solid copper metal and aqueous zinc sulfate.
Zinc + copper(II) sulfate  copper + zinc sulfate
Zn(s) + CuSO4(aq)  Cu(s) + ZnSO4(aq)

8. Balancing Equations
In a chemical equation, the law of conservation of mass is satisfied by “balancing” the number of atoms of each element in the reactants and products.

9. Coefficient  subscript = # of atoms
Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
Add coefficients to make #s equal.
*Coefficient-small whole number that appears in front of a formula in a chemical eqn.
Coefficient  subscript = # of atoms
4. Reduce coefficients to lowest possible ratio, if necessary.
5. Double check atom balance!!!

10. Helpful Tips Balance one element at a time.
Update ALL atom counts after adding a coefficient.
If an element appears more than once per side, balance it last.
Balance polyatomic ions as single units.
“1 SO4” instead of “1 S” and “4 O”

11. 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

12. Balancing Examples H2O2(aq)  O2(g) + H2O(l)
Cu(s) + AgNO3(aq)  Ag(s) + Cu(NO3)2(aq)
Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq)
Zn(s) + CuSO4(aq)  Cu(s) + ZnSO4(aq)

13. 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.

14. Review
Write balanced chemical equations for each of the following reactions:
Solid sodium combines with chlorine gas to produce solid sodium chloride.
When solid copper reacts with aqueous silver nitrate, the products are aqueous copper(II) nitrate & solid silver.
In a blast furnace, the reaction between solid iron(III) oxide & carbon monoxide gas produces solid iron & carbon dioxide gas.
2Na(s) + Cl2(g)  2NaCl(s)
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Fe2O3(s) + 3CO(g)  2Fe(s) + 3CO2(g)

15. Types of Chemical Reactions

16. Classifying reactions
Enables us to predict the products of reactions
5 basic types:
Synthesis
Decomposition
Single-replacement
Double-replacement
Combustion

17. A + B  AB Synthesis AKA composition/ formation reaction
the combination of 2 or more substances to form a compound
only one product
A + B  AB

18. Synthesis
H2(g) + Cl2(g)  2HCl(g)

19. Example Mg(s) + O2(g) ? Mg(s) + O2(g)  MgO (unbalanced!)
Type-synthesis
Form ionic compound (metal & non)criss cross charges
Mg+2 O-2  MgO
Mg(s) + O2(g)  MgO (unbalanced!)
2Mg(s) + O2(g)  2MgO

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

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

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

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

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

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

26. CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Combustion
the burning of any substance in O2 to produce carbon dioxide and water vapor
A + O2  B
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

27. Combustion C3H8(g)+ O2(g)  5 3 4 CO2(g)+ H2O(g) Predicting Products:
contain oxygen
hydrocarbons form CO2 + H2O
C3H8(g)+ O2(g) 
CO2(g)+ H2O(g)

28. Classify each rxn: N2(g) + 3H2(g)  2NH3(g)
2C6H14(l) + 19O2(g)  12CO2(g) + 14H2O(g)
AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)
Synthesis
Combustion
Double replacement

29. Activity Series of the Elements

30. Predicting products: single replacement rxns
A + BC  B + AC
To determine if A will replace B in compound BC, use the activity series
Activity series-list of elements organized according to the ease with which the elements undergo certain chemical reactions.
An element can replace any element below it in the series.

31. Example Al(s) + ZnCl2(aq) ?
Type-single replacement
What is replacing what?
Al replacing Zn
Will this happen? Check to see if Al is more active than Zn.
Al is above Zn, so it is more active
Al(s) + ZnCl2(aq)  Zn(s) + AlCl3(aq) (unbalanced)
2Al(s) + 3ZnCl2(aq)  3Zn(s) + 2AlCl3(aq)

32. Example Co(s) + 2NaCl(aq) ? Co(s) + 2NaCl(aq)  no rxn (NR)
Type-single replacement
What is replacing what?
Co replacing Na
Will this happen? Check to see if Co is more active than Na.
Co is NOT above Na in the activity series, so it will NOT replace Na.
Co(s) + 2NaCl(aq)  no rxn (NR)

33. Review
Using the activity series, predict whether each of the possible reactions will occur. For reactions that will occur, write the products & balance the eqn.
MgCl2(aq) + Zn(s) No reaction
2Al(s) + 3H2O(g)  Al2O3(s) + 3H2(g
2Cd(s) + O2(g)  2CdO(s)
I2(s) + KF(g) No reaction