1. Chemical Reactions
Chapter 11

2. Describing Chemical Reactions
Essential Question:
How does one write a proper word, skeleton or chemical equation?

3. Writing Chemical Equations
How do you describe what has happened in a chemical reaction?
Recall from Chapter 2 the shorthand method of describing a chemical reaction:
Reactants Products

4. Word Equations iron + oxygen Iron(III) oxide
hydrogen peroxide water + oxygen
methane + oxygen carbon dioxide water
What does the arrow in these word equations indicate?

5. Skeleton Equations Fe + O2 Fe2O3 H2O2 H2 + O2 CH4 + O2 CO2 + H2O
A skeleton equation is an equation that does not indicate the relative amounts of the substance involved.

6. Balancing Chemical Equations
How would you write a word equation for the production of a tricycle?
frame + wheel + handlebar + pedal
tricycle
This doesn’t tell about the relative amounts involved

8. This still doesn’t tell about the relative amounts involved
Skeleton Equations
How would you write a skeleton equation for the production of a tricycle?
F + W + H + P FW3H2P2
Notice:
This still doesn’t tell about the relative amounts involved

9. Bicycle Equation

10. You must use coefficients to indicate the relative amounts involved.
Balanced Equations
How would you write a balance chemical equation for the production of a tricycle?
F + 3W + 2H + 2P FW3H2P2
Notice:
You must use coefficients to indicate the relative amounts involved.

11. Balancing Chemical Reactions

12. Combustion of Methane

13. Production of Hydrogen Chloride

14. Rules for Writing Balanced Chemical Equations
See the table at the top of page 327.
Balancing Chemical Equations –
Computer lab activity

16. Balance These Equations
AgNO3 + H2S Ag2S + HNO3
Zn(OH)2 + H3PO Zn3(PO4)2 + H20
FeCl3 + Ca(OH)2 Fe(OH)3 + CaCl2
Ag2S(s) + Al(s) Ag(s) + Al2S3(g)

17. Types of Chemical Reactions
Essential Question:
What are the five general types of chemical reactions, and how can you predict the products of these reactions?

18. Classifying Reactions
Reactions fall into five general categories:
Combination Reactions
Decomposition Reactions
Single Replacement Reactions
Double Replacement Reactions
Combustion Reactions

19. Combination Reactions
Two or more substances forming a single new substance.
Our analogy: like a marriage
What distinguishes combination reactions is the presence of only one product.

20. Combination Reactions

21. Combination Reactions
Also known as Synthesis reactions.
Examples:
2Mg(s) + O2(g) 2MgO
2K(s) + Cl2(g) 2KCl(s)
Fe(s) + S(s) FeS(s)
2Fe (s) + 3S(s) Fe2S3(s)

22. Decomposition Reactions
A single compound breaks down into two or more simpler products.
Our analogy: a divorce
What distinguishes a decomposition reaction is a single reactant.

23. Decomposition Reactions

24. Decomposition Reactions
Examples:
2HgO(s) 2Hg(l) + O2(g)
2H2O (l) 2H2 (g) + O2(g)
2HI H2(g) + I2(s)
electricity

25. Single-Replacement Reactions
One element replaces another element in a compound.
Our analogy: Date-stealing
What distinguishes a S-R reaction is an uncombined element in the reactants with a different uncombined element in the products.

26. Single-Replacement Reactions
Examples:
Fe(s) + Pb(NO3)2(aq)
Fe(NO3)2(aq) + Pb(s)
Cl2(g) + 2NaI(aq)
2NaCl(aq) + I2(aq)

27. Single-Replacement

28. Will S-R Reactions Occur?
Whether one metal will replace another in a compound depends their respective reactivities.
A reactive metal will replace any metal below it in the reactivity series.
See Table 11.2 on page 333.
What about the reactivity of the halogens?

29. Activity Series of the Metals

30. The Activity Series of the Metals

31. Double-Replacement Reactions
A chemical change involving an exchange of positive ions between two compounds.
Our analogy: Date-Swapping

32. Double-Replacement

33. Double-Replacement Reactions
Examples:
Na2S(aq) + Cd(NO3)2(aq)
CdS(s) + 2NaNO3(aq)
2NaCN(aq) + H2SO4(aq)
2HCN(g) + Na2SO4(aq)
Ca(OH)2(aq) + 2HCl(aq)
CaCl2(aq) + 2H2O(l)

34. Double-Replacement Reactions
For a D-R reaction to occur, one of the following is usually true:
One of the products is a solid that precipitates out
One of the products is a gas
One of the products is a molecular compound, such as water

35. Combustion Reactions
An element or a compound reacts with oxygen, often producing light and heat.
Complete combustion = a hydrocarbon reacting with oxygen to produce ONLY carbon dioxide and water as the products.

36. Combustion Reactions

37. Which of these are complete combustion?
Examples:
2C8H18(l) + 25O2(g)
16CO2(g) + 18H2O(l)
2C6H6(l) + 15O2
12CO2(g) + 6H2O(g)
2Mg(s) + O2(g) 2MgO(s)
Which of these are complete combustion?

44. Reactions in Aqueous Solution
Essential Question:
What does a net ionic equation show, and how can one predict the formation of a precipitate in a double-replacement reaction?

45. Net Ionic Equations
A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge.
All ions that are unchanged from the reactants side to the products side of the equation are eliminated.

46. Net Ionic Equations Begin with a double-replacement reaction:
AgNO3(aq) + NaCl(aq)
AgCl(s) + NaNO3(aq)
Write the complete ionic equation:
Ag+(aq) + NO3–(aq) + Na+ (aq) + Cl– (aq)
AgCl(s) + Na+(aq) + NO3– (aq)

47. Net Ionic Equations, cont.
Eliminate the ions that are “spectators”
Ag+(aq) + NO3–(aq) + Na+ (aq) + Cl– (aq)
AgCl(s) + Na+(aq) + NO3– (aq)
What remains is the Net Ionic Equation
Ag+(aq) + Cl– (aq) AgCl(s)

48. Formation of Precipitates
One can predict the formation of a precipitate by using the general rules for solubility for ionic compounds.
See Table 11.3 on page 344, or see the Reference Tables.

49. Solubility Rules for Ionic Compounds

50. Predicting the Formation of a Precipitate

51. Formation of Precipitates
Will a precipitate form when the following aqueous solutions are mixed?
AgNO3 and Na2SO4
NH4Cl and Ba(NO3)2
CaCl2 and K2SO4
Hg(NO3)2 and HCl
Yes, No, Yes, No