1. CH.3 Balancing Reactions Reaction Types

2. A Chemical Reaction Reactants Products Types of Chemical reactions:
There are many types of reactions but
most can be classified into a few simple
reactions types.
How do you know a chemical reaction has occurred?

3. Chemical equations Chemist’s shorthand to describe a reaction.
It shows:
All reactants and products
The state of all substances
Any conditions used in the reaction
CaCO3 (s) CaO (s) CO2 (g) 
Reactant Products
A balanced equation shows the relationship
between the quantities of all reactants and products.

4. Balancing chemical equations
Each side of a chemical equation must have the same number of each type of atom.
CaCO3 (s) CaO (s) + CO2 (g)
Reactants Products
1 Ca Ca
1 C C
3 O O

5. Balancing chemical equations
Step 1 Count the number of atoms of each element on each side of the equation.
Step 2 Determine which atom numbers are not balanced.
Step 3 Balance one atom at a time by using coefficients in front of one or more substances.
Step 4 Repeat steps 1-3 until everything is balanced.

6. Chemical Changes Temperature Changes Light Gas formation Precipitation
Color changes

7. Types of Chemical Reactions
Reactions involving electron transfer
synthesis or combination
decomposition
Electrochemical or single replacement
Combustion of hydrocarbons.
Reactions that involve rearrangement but not necessarily involve electron transfer
Metathesis or Double Substitution
Precipitation reactions and
Acid Base Reactions
Polymerization reaction

8. Properties of aqueous solutions
There are two general classes of solutes.
Electrolytic
ionic compounds in polar solvents
dissociate in solution to make ions
conduct electricity
may be strong (100% dissociation) or weak (less than 100%)
Nonelectrolytic
do not conduct electricity
solute is dispersed but does not dissociate

9. Dissolving ionic compounds
When an ionic solid dissolves in water, the solvent removes ions from the crystal.
NaCl + H2O  Na+(aq) + Cl- (aq)

10. Dissolving covalent compounds
Covalent compounds do not dissociate.
C6H12O6  C6H12O6 (aq)

11. Ionic equations
When ionic substances dissolve in water, they dissociate into ions.
AgNO Ag+ + NO3-
KCl K+ + Cl-
When a reaction occurs, only some of the ions are actually involved in the reaction.
Ag+ + NO K+ + Cl AgCl(s) + K+ + NO3-
H2O
H2O

12. Ag+ + NO3- + K+ + Cl- AgCl(s) + K+ + NO3-
Ionic equations
To help make the reaction easier to see, we commonly list only the species actually involved in the reaction.
Molecular equation
KCl + AgNO3 AgCl(s) + KNO3
Full ionic equation
Ag+ + NO K+ + Cl AgCl(s) + K+ + NO3-
Net ionic equation
Ag+ + Cl AgCl(s)
NO3- and K+ are referred to as spectator ions.

13. Some simple solubility rules
All acids are soluble.
All Na+, K+ and NH4+ salts are soluble.
All nitrate and acetate salts are soluble.
All chlorides except AgCl and Hg2Cl2 are soluble. PbCl2 is slightly soluble.
All sulfates are soluble except PbSO4, Hg2SO4, SrSO4 and BaSO4. Ag2SO4 and CaSO4 are slightly soluble.
All sulfides are insoluble except those of the Group IA (1), IIA (2) and ammonium sulfide.
All hydroxides are insoluble except those of the group IA(1) and Ba(OH)2. Sr(OH)2 and Ca(OH)2 are slightly soluble.

14. Metathesis Reactions Precipitation reactions
the formation of a solid upon mixing two solutions.
Gas formation
The formation of a gas when two mixtures are reacted
Acid Base titration
The neutralization of acids and bases to form a salt in water.

15. Precipitation NaCl + AgNO3 = AgCl (ppt) + NaNO3
Pb(NO3)2 + K2CrO4 = PbCrO4 (ppt) + KNO3

16. Gas Formation Vinegar + Baking soda = Carbon dioxide
CH3COOH + NaHCO3 = NaCH3COO + H2O + CO2

17. Acid Base Neutralization
Vinegar + Ammonia = Salt + water
CH3COOH + NH4OH = NH4CH3COO + H2O

18. Common REDOX Reactions
Combustion
Corrosion
Photosynthesis
Kreb’s Cycle
Synthesis and Decomposition
Single Replacement

19. Oxidation numbers and the periodic table
Some observed trends in compounds.
Metals have positive oxidation numbers.
Transition metals typically have more than one oxidation number.
Nonmetals and semimetals have both positive and negative oxidation numbers.
No element exists in a compound with an oxidation number greater than +8.
The most negative oxidation numbers equals 8 - the group number

20. Oxidation Numbers
1. An atom in its elemental state has an oxidation number of 0.
2. An atom in a monatomic ion has an oxidation number identical to its charge.
3. An atom in a polyatomic ion or in a molecular compound usually has the same oxidation number it would have it were a monatomic ion.
4. The sum of the oxidation numbers is 0 for a neutral compound and equal to the net charge for a polyatomic ion.

21. Identifying oxidation-reduction reactions.
Oxidation-Reduction - REDOX
A chemical reaction where there is a net change in the oxidation number of one or more species.
Both an oxidation and a reduction must occur during the reaction.
Mg (s) + Cl2 (g) MgCl2 (s)
Here the oxidation number of Mg has changed from
zero to +2. Cl has changed from zero to -1.

22. 2 Fe(NO3)3 (aq) + Zn(s) 2 Fe(NO3)2 (aq) + Zn(NO3)2 (aq)
REDOX reactions
Oxidation
An increase in oxidation number.
Reduction
A decrease in oxidation number.
If the oxidation number of any element changes in the course of a reaction, the reaction is oxidation-reduction.
Example.
2 Fe(NO3)3 (aq) + Zn(s) Fe(NO3)2 (aq) + Zn(NO3)2 (aq)

23. Half Reactions The reactions that show the loss or gain of electrons.
2 Mg + O2  2 MgO
What are the oxidation states of each of the atoms in the above reaction?
Mg  Mg+2
O2  2 O2-

24. Oxidation 2 Mg + O2  2 MgO Mg  Mg+2 12 p, 12 e 12 p, 10 e
Mg  Mg e
The loss of electrons

25. Single replacement reaction
Where one element displaces another in a chemical compound.
H2 + CuO Cu + H2O
In this example, hydrogen replaces copper.
This type of reaction always involves oxidation and reduction (REDOX).
Since one species is replacing another, there are no spectator ions.

26. Single Replacement

27. Synthesis Reaction
The formation of a new compound from several substances
2 H2 + O2 = 2 H2O
2 Na + Cl2 = 2 NaCl
CaO (lime water) + CO2 = CaCO3 (s)

28. Synthesis

29. Decomposition Reactions
HgO = Hg + O2
H2O2= H2O + O2
with MnO2 catalyst

30. 1774: Antoine Lavoisier solves the question of the burning process and chemical processes

31. Combustion The burning of a substance in the presence of oxygen.
Gasoline burns when oxygen is taken into your engine, the products of the reaction are carbon dioxide and water
C8H O2 = CO2 + H2O
Fe + O2 = Fe2O3 (rust)