1. Chemical Reactions
Chapter 8

2. Chemical Change In a chemical change,
reacting substances form new substances with different compositions and properties
a chemical reaction takes place 2

3. Chemical Reactions (continued)
In a chemical reaction,
old bonds are broken and new bonds formed
atoms in the reactants are rearranged to form one or more different substances 3

4. 4

5. Chemical Equations A chemical equation
gives the chemical formulas of the reactants on the left of the arrow and the products on the right.

6. Reactants – beginning substances in a chemical reaction
Products – new substances produced as a result of a chemical reaction

8. In a chemical reaction,
Atoms are not gained or lost.
The number of atoms in the reactants is equal to the number of atoms in the products.

9. Chemical equations must be balanced to show that atoms are not gained or lost during chemical reactions.
Al + S Al2S3
This equation is NOT balanced
The number of Al and S atoms on each side of the arrow are not the same.

10. The chemical formulas cannot be changed.
However, the number of atoms, molecules or formula units can be increased to balance this equation.
coefficient - a small whole number that appears in front of a formula in a balanced chemical

11. Al S Al2S Not Balanced
2 Al S Al2S3 Balanced
reactants products
2 Al = Al
3 S = S

12. Learning Check State the number of atoms of each element on the
reactant side and the product side for each of the
following balanced equations:
A. P4(s) + 6Br2(l) → 4 PBr3(g)
B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)

13. Solution A. P4(s) + 6Br2(l) → 4PBr3(g) phosphorus - 4 bromine - 12
B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
aluminum - 2
iron - 2
oxygen -3

14. Learning Check Determine if each equation is balanced or not.
A. Na(s) + N2(g) → Na3N(s)
B. C2H4(g) + H2O(l) → C2H5OH(l)

15. Solution Determine if each equation is balanced or not.
A. Na(s) + N2(g) → Na3N(s)
No. 2N on reactant side, 1N on product side.
1Na on reactant side, 3Na on product side.
Correctly balanced: 6Na(s) +N2(g) → 2Na3N(s)
B. C2H4(g) + H2O(l) → C2H5OH(l)
Yes. 2C = 2C
6H = 6H
1O = 1O

16. Guide to Balancing Equations
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

17. STEP 1 Write the equation with the correct formulas.
NH3(g) + O2(g) NO(g) + H2O(g)
STEP 2 Determine if the equation is balanced.
No, not all atoms are balanced.
STEP 3 Balance with coefficients in front of formulas.
4NH O2 4NO + 6H2O
STEP 4 Check that atoms of each element are equal in
reactants and products.
4 N (4 x 1N) = N (4 x 1N)
12 H (4 x 3H) = 12 H (6 x 2H)
10 O (5 x 2O) = 10 O (4O + 6O)

18. Learning Check Check the balance of atoms in the following:
Fe3O4(s) H2(g) Fe(s) H2O(l)
A. Number of H atoms in products.
1) 2 2) 4 3) 8
B. Number of O atoms in reactants.
C. Number of Fe atoms in reactants.
1) 1 2) 3 3) 4

19. Solution Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)
A. Number of H atoms in products.
3) 8 (4H2O)
B. Number of O atoms in reactants.
2) 4 (Fe3O4)
C. Number of Fe atoms in reactants.
2) 3 (Fe3O4)

20. Learning Check
Balance each equation and list the coefficients in the balanced equation going from reactants to products:
A. ___ Mg (s) + ___ N2 (g) __ Mg3N2 (s)
1) 1, 3, ) 3, 1, ) 3, 1, 1
B. __ Al (s) + __ Cl2 (g) __ AlCl3 (s)
1) 3, 3, 2 2) 1, 3, ) 2, 3, 2

21. Solution A. 3) 3, 1, 1 3 Mg(s) + N2(g) Mg3N2(s) B. 3) 2, 3, 2
2 Al(s) Cl2(g) AlCl3(s)

22. Balancing with Polyatomic Ions
Na3PO4 (aq) + MgCl2 (aq) NaCl (aq) + Mg3(PO4)2 (s)
Balance PO43- as a unit
2Na3PO4 (aq) Mg3(PO4)2 (s)
2PO = PO43-
Balance Mg
3MgCl2 (aq) Mg3(PO4)2 (s)
3Mg = Mg2+
Balance Na and Cl to complete balanced equation
3MgCl2 (aq) + 2Na3PO4 (aq) NaCl (aq) + Mg3(PO4)2 (s)
6Na = Na+
6Cl = Cl-

23. Learning Check
Balance and list the coefficients from reactants to products:
A. __Fe2O3(s) __C(s) __Fe(s) __CO2(g)
1) 2, 3, 2, ) 2, 3, 4, ) 1, 1, 2, 3
B. __Al(s) + __FeO(s) __Fe(s) __Al2O3(s)
1) 2, 3, 3, ) 2, 1, 1, ) 3, 3, 3, 1
C. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)
1) 3, 2, 1, ) 2, 3, 1, ) 2, 3, 2, 3

24. Solution A. 2) 2, 3, 4, 3 2 Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g)
B. 1) 2, 3, 3, 1
2 Al(s) + 3FeO(s) Fe(s) + Al2O3(s)
C. 2) 2, 3, 1, 3
2Al(s) + 3H2SO4(aq) Al2(SO4)3(aq) + 3H2(g)

25. Types of Chemical Reactions
Chapter 8 section 2

26. Type of Reactions Chemical reactions can be classified as
Combination reactions.
Decomposition reactions.
Single Replacement reactions.
Double Replacement reactions.
Combustion reactions

27. Combination
In a combination reaction - two or more elements (or simple compounds) combine to form one product

28. combination 2Mg(s) + O2(g) 2MgO(s) 2Na(s) + Cl2(g) 2NaCl(s)
SO3(g) + H2O(l) H2SO4(aq)

29. Decomposition
In a decomposition reaction, one substance splits into two or more simpler substances.

30. decomposition
2HgO(s) 2Hg(l) + O2(g)
2KClO3(s) 2KCl(s) + 3O2(g)

31. Learning Check Classify the following reactions as
combination or decomposition:
A. H2(g) + Br2(g) HBr(l)
B. Al2(CO3)3(s) Al2O3(s) + 3CO2(g)
C. 4Al(s) + 3C(s) Al4C3(s)

32. Solution
Classify the following reactions as combination decomposition:
A. H2(g) + Br2(g) HBr(l)
combination
B. Al2(CO3)3(s) Al2O3(s) + 3CO2(g)
decomposition
C. 4Al(s) + 3C(s) Al4C3(s)

33. Single Replacement
In a single replacement reaction, one element takes the place of a different element in a reacting compound.

34. Single replacement Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

35. Double Replacement
In a double replacement reaction, two elements in the reactants exchange places.

36. double replacement AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
ZnS(s) HCl(aq) ZnCl2(aq) + H2S(g)

37. Learning Check
Classify the following reactions as single replacement or double replacement
2Al(s) + 3H2SO4(aq) Al2(SO4)3(s) + 3H2(g)
Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq)
C. 3C(s) + Fe2O3(s) Fe(s) CO(g)

38. Solution A. 2Al(s) + 3H2SO4(aq) Al2(SO4)3(s) + 3H2(g)
single replacement
B. Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq)
double replacement
C. 3C(s) + Fe2O3(s) Fe(s) CO(g)

39. Combustion Reaction
In a combustion reaction, an element or compound reacts with oxygen, often producing energy in the form of heat and light.
4Fe + 3O Fe2O3
2 C4H O CO2 + 10H2O

40. Learning Check Identify each type of chemical reaction
A. 3Ba(s) + N2(g) Ba3N2(s)
B. 2Ag(s) + H2S(aq) Ag2S(s) + H2(g)
C. SiO2(s) + 4HF(aq) SiF4(s) + 2H2O(l)
D. PbCl2(aq) + K2SO4(aq) KCl(aq) + PbSO4(s)
E. K2CO3(s) K2O(aq) + CO2(g)
F. S (s) + O2 (g) SO2 (g)

41. Solution Combination Single replacement Double replacement
Decomposition
Combustion (also combination)

42. Activity Series
A reactive element will replace any element listed below it on the activity series.
* Metals from Li to Na will replace H from acids and water; from Mg to Pb they will replace H from acids only

43. Electrolysis
Electrolysis is a process by which electrical energy is used to produce a chemical change.
2H2O(l) H2(g) + O2(g)

44. Electrolysis Continued

45. Reactions in Aqueous Solution
Chapter 8 section 3

46. aqueous solution – water is the solvent
Most ionic compounds dissociate or separate into cations and anions when placed in water.

47. AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)
Complete ionic equation – an equation that shows dissolved ionic compounds as their free ions.
Ag+ (aq) + NO3 - (aq) + Na + (aq) + Cl - (aq)
AgCl (s) Na + (aq) + NO3 - (aq)
A chemical reaction occurred because there was the formation of a precipitate.

48. precipitate – insoluble salt
Ag+ (aq) + NO3 - (aq) + Na + (aq) + Cl - (aq)
AgCl (s) Na + (aq) + NO3 - (aq)
precipitate – insoluble salt
In the above equation you can see that AgCl (s) is a solid.
The above equation can be simplified by eliminating the ions that do not participate in the chemical reaction

49. spectator ions – ions not directly involved in the chemical reaction
Ag+ (aq) + NO3 - (aq) + Na + (aq) + Cl - (aq)
AgCl (s) Na + (aq) + NO3 - (aq)
net ionic equation – equation that shows only those particles that take part in the reaction.
spectator ions – ions not directly involved in the chemical reaction
net ionic equation is a chemical equation with the spectator ions removed

50. Which ions are the spectator ions? Na+ + NO3 -
Ag+ (aq) + NO3 - (aq) + Na + (aq) + Cl - (aq)
AgCl (s) Na + (aq) + NO3 - (aq)
Which ions are the spectator ions?
Na NO3 -
What is the net ionic equation?
Ag + (aq) + Cl - (aq) AgCl (s)

51. What is the spectator ion? Net ionic equation:
Net ionic equations must be balanced with respect to charge as well as number of atoms.
Pb (s) + AgNO3 (aq) Ag(s) + Pb(NO3) 2 (aq)
What is the spectator ion?
NO3-
Net ionic equation:
Pb (s) + 2Ag Ag (s) Pb2+