1. Chemical Reactions
Chapter 3

2. Learning Objectives Students understand
The significance and uses of balanced chemical equations
The nature and characteristics of chemical equilibrium
The nature of ionic substances dissolved in water
Oxidation-reduction reactions and the three types of exchange reactions
Acid-base reactions involve the transfer of hydrogen ions

3. Learning Objectives Students will be able to
Balance chemical equations
Predict solubility and species present
Recognize common types of reactions and predict products
Know names and formulas of common acids & bases
Write a net ionic equation
Determine oxidation numbers

4. 3.1 Chemical Equations
the reactants are written to the left and the products are written to the right of the arrow
s, g, l, aq indicate the states of matter
coefficients are used to show the relative amounts
the law of conservation of matter (Antoine Lavoisier)

5. Chemical Equations balanced equations vs. skeleton equations
relationship between amounts is stoichiometry
stoichiometric coefficients indicate number of atoms, molecules, formula units, or moles

6. 3.2 Balancing
Formulas for reactants and products have to be written correctly
Subscripts cannot be changed to balance

7. Balancing Combustion
Step 1: write correct formulas for reactants and products
Step 2: balance the carbon atoms
Step 3: balance the hydrogen atoms
Step 4: balance the oxygen atoms
Step 5: verify atoms are balanced

8. Combustion Reactions
Complete oxidation of an organic compound to yield CO2 and H2O
C2H4(g) + 3O2(g)  2CO2(g) + 2H2O(l)
Nonmetallic hydrides combine with oxygen to form oxides and water
SiH4(g) + 2O2(g)  SiO2(s) + 2H2O(l)
Nonmetallic sulfides combine with oxygen to form sulfur dioxide and oxides
CS2(s) + 3O2(g)  CO2(g) + 2SO2(g)

9. 3.3 Chemical Equilibrium
Reactions are reversible, and many reactions lead to incomplete conversion of reactants to products.
Chemical equilibrium is when no macroscopic change is observed.
Dynamic equilibrium indicates the forward and reverse reactions are occurring at equal rates.

10. Chemical Equilibrium
Depending upon different factors, product-favored reactions are reactions in which reactants are largely converted to products at equilibrium.
Reactant-favored reactions mean that at equilibrium only a small amount of reactants have been converted to products.

11. 3.4 Reactions in Aqueous Solution
Another name for a solution is a homogeneous mixture.
solute and solvent
Substance dissolved in water are called aqueous solutions.
Polarity of water creates an attraction for ions.
Water molecules surround each ion in the dissolved substance.

12. Reactions in Aqueous Solutions
Four major categories of chemical reactions:
synthesis
decomposition
oxidation-reduction
acid-base reactions

13. Ions and Molecules
Compounds that conduct electricity in aqueous solution are called electrolytes.
All ionic compounds that are soluble in water are electrolytes.
Strong electrolytes completely ionize in solution. (such as salt)
Weak electrolytes only partially dissociate. (such as acetic acid)
Nonelectrolytes dissolve in water but don’t ionize. (such as sugar)
Most molecular compounds that dissolve in water are nonelectrolytes.

14. Solubility of Ionic Compounds in Water
Although many ionic compounds dissolve completely, some dissolve only to a small extent and some are essentially insoluble.
Solubility rules on page 108

15. 3.5 Precipitation Reactions
precipitation reactions form insoluble products (precipitate)
lead nitrate and potassium iodide
products can be predicted using solubility rules

16. Net Ionic Equations net ionic equations leave out the spectators
Strong acids, strong bases, and soluble salts exist as ions in solution
All other species are represented by their complete formulas (weak acids, weak bases, insoluble salts, etc.)

17. Net Ionic Equations
Write a complete, balanced equation and indicate the state of each substance.
Rewrite the whole equation, ionizing species where appropriate (only aq)
Cross off spectators
Mass and charge balance!

18. Practice Problems
Write a balanced net ionic equation for each of the following reactions:
AlCl3 + Na3PO4 AlPO4 + NaCl
Solutions of iron (III) chloride and potassium hydroxide give iron (III) hydroxide and potassium chloride when combined.
Solutions of lead (II) nitrate and potassium chloride give lead (II) chloride and potassium nitrate when combined.

19. Practice Problems
Write balanced, net ionic equations for each of these reactions that occur between aqueous solutions.
CaCl2 + Na3PO4
Iron(III) chloride and potassium iodide
Lead(II) nitrate and potassium chloride

20. 3.6 Acids and Bases Properties of acids and bases
Reactivity
Taste
indicators
Common Acids and Bases p. 115

21. Arrhenius Acids and Bases
Focuses on formation of hydrogen and hydroxide ions in solution
An acid, when dissolved in water, increases the concentration of hydrogen ions, H+, in solution.
A base, when dissolved in water, increases the concentration of hydroxide ions, OH-, in solution.

22. Arrhenius Acids and Bases
The reaction of an acid and a base produces a salt and water. Acid-base reactions were logically described as resulting from the combination of H+ and OH- to form water.
Proposed that acid strength was related to the extent to which the acid ionized – strong vs. weak acids and bases

23. Brønsted-Lowry Acids and Bases
Viewed acids and bases in terms of the transfer of a proton (H+)
Described in terms of equilibria
An acid is a proton-donor.
A base is a proton-acceptor.
An acid-base reaction involves the transfer of a proton from an acid to a base to form a new acid and a new base.

24. Brønsted-Lowry Acids and Bases
Amphiprotic – species that can function as either an acid or a base

25. Brønsted-Lowry Acids and Bases
Acids capable of transferring two or more H+ ions react with water in multiple steps. Different steps may favor different sides of equilibrium.
Sulfuric acid is capable of transferring two protons. The first step is product-favored but the second step is reactant-favored.

26. Practice Problem
Write a balanced equation for the reaction that occurs when H3PO4 donates a proton to water to form the dihydrogen phosphate ion.
Write a net ionic equation showing the dihydrogen phosphate ion acting as an acid in a reaction with water.

27. Reactions of Acids and Bases
Acids and bases usually react to produce a salt (any ionic compound whose cation comes from a base and whose anion comes from an acid) and water.
Neutralization Reactions

28. Oxides of Nonmetals and Metals
Oxides of nonmetals such as CO2, SO2, SO3, and NO2 that react with water to produce an acidic solution are called acidic oxides.
Oxides of metals are called basic oxides because they produce basic solutions in water, such as CaO.

29. Oxides of Nonmetals and Metals
metal oxide + nonmetal oxide  salt
6CaO(s) + P4O10(s)  2Ca3(PO4)2(s)

30. Homework
After reading Sections , you should be able to do the following…
P. 137b-c (15-16, 19-20, 32-33, 37-40)