1. Modern Chemistry Chapter 8 Chemical Equations and Reactions

2. Describing Chemical Reactions
Section 1
Describing Chemical Reactions

3. Indications of a Chemical Reaction
Proof: one or more substances has changed identity – chemical change
Evolution of energy as heat and/or light
Production of a gas
Formation of a precipitate
Color change

4. Indications of a Reaction

5. Characteristics of a Chemical Reaction
The equation must represent known facts.
The equation must contain the correct formulas for the reactants and products.
Diatomic elements: I2 Br2 Cl2 F2 O2 N2 H2
Molecular elements: S8 P4 (page 263)
The law of conservation of mass must be satisfied.
Coefficients – a whole number that appears in front of a formula in a chemical equation.

6. Diatomic Elements
p. 263

7. Nitrogen gas molecules

8. A Collection of Argon Atoms

9. Word and Formula Equations
Word equations – reactants & products expressed in words
methane + oxygen  carbon dioxide + water
REACTANTS
PRODUCTS
YIELDS

10. Word and Formula Equations
Formula equations – reactants & products expressed with formulas – not balanced
methane + oxygen  carbon dioxide + water
CH4 (g) O2 (g)  CO2 (g) H2O(g)
STATE OF MATTER SYMBOLS
Solid (s) Liquid (l) Gas (g) Aqueous (aq)
 Dissolved in water

11. Methane Combustion

12. Additional Symbols
p. 226

13. Additional Symbols
p. 226

14. Balancing Chemical Equations
If the reaction is described by a paragraph, write the word equation.
Write the formula for each reactant and product to get the formula equation.
Balance the equation.
Insert state of matter symbols and other additional symbols.

15. Balancing Chemical Equations
GOAL OF THE GAME:
To get the same number of atom of each element in the reactant and the product.
To obey the law of conservation of mass.

16. Balancing Chemical Equations
RULES OF THE GAME:
Only coefficients can be added or changed.
Once formulas are written subscripts can not be changed.

17. Balancing Chemical Equations
TIPS FOR PLAY:
Balance the different types of atoms one at a time.
First balance elements that appear only once on each side.
Balance polyatomic ions that appear on both sides as a single unit.
Balance H and O last.
page 271

18. Balancing Chemical Equations
TIPS FOR PLAY:
Try keeping a tally for each element on each side below the equation.
If it could be balanced by a coefficient of 1½ - use it- multiply all coefficients in the equation by 2.

19. Sample Problem
The reaction of zinc with aqueous hydrochloric acid produces a solution of zinc chloride and hydrogen gas. Write a balanced equation for the reaction

20. zinc + hydrochloric acid  zinc chloride + hydrogen
Sample Problem p.272
zinc + hydrochloric acid  zinc chloride + hydrogen
Zn HCl  ZnCl H2 2 H Cl Zn H Cl Cl Zn H
Zn (s) + 2HCl (aq)  ZnCl2 (aq) + H2 (g)

21. Writing Equations
Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride.
How many?
Of what?
In what state?

22. Writing Equations  2 Al
(s)
+ 3
CuCl2
(aq)
(s)
(aq)
3Cu
+ 2
AlCl3

23. Sample Problem
Solid aluminum carbide, reacts with water to produce methane gas, CH4, and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.

24. aluminum carbide + water  methane + aluminum hydroxide
Sample Problem p.273
aluminum carbide + water  methane + aluminum hydroxide
Al4C H2O  CH Al(OH)3 12 3 4
Al =
C =
H =
O = 4 3 24 12 4 3 2 1
Al =
C =
H =
O = 4 3 24 12 1 7 3 4 1 16 12
Al4C3 (s) + 12H2O (l)  3CH4 (g) + 4Al(OH)3 (s)

25. Sample Problem
Aluminum sulfate and calcium hydroxide are used in water-purification process. When added to water, they dissolve and react to produce two insoluble products, aluminum hydroxide and calcium sulfate. These products settle out, taking suspended solid impurities with them. Write a balanced chemical equation for the reaction.

26. Al2(SO4 )3 + Ca(OH)2  Al(OH)3 + CaSO4
Sample Problem p.273
aluminum sulfate + calcium hydroxide  aluminum hydroxide + calcium sulfate
Al2(SO4 ) Ca(OH)2  Al(OH)3 + CaSO4 3 2 3
Al =
SO4 =
Ca =
OH = 2 3 6 2 3 1
Al =
SO4 =
Ca =
OH = 2 1 6 2 3 6 1 3
Al2(SO4)3(aq) + 3Ca(OH)2(aq)  2Al(OH)3(s) + 3CaSO4(s)

27. Practice Problems
Write word, formula, and balanced chemical equations for each of the following reactions:
Magnesium and hydrochloric acid react to produc magnesium chloride and hydrogen.
Aqueous nitric acid reacts with solid magnesium hydroxide to produce aqueous magnesium nitrate and water

28. Practice Problems
2. Solid calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas. Write a balanced chemical equation for this reaction.

29. Practice Problems
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 and solid silver
In a blast furnace, the reaction between solid iron (III) oxide and carbon monoxide gas produces solid iron and carbon dioxide gas.

30. Describing Equations Describing Coefficients: individual atom = “atom”
covalent substance = “molecule”
ionic substance = “ formula unit”
3CO2 
2Mg 
4MgO 
3 molecules of carbon dioxide
2 atoms of magnesium
4 formula units of magnesium oxide

31. Describing Equations Describing Coefficients:
Also moles for EVERY type
3CO2 
2Mg 
4MgO 
3 moles of carbon dioxide
2 moles of magnesium
4 moles of magnesium oxide

32. Significance of a Equation
4 Fe (s) + 3O2 (g)  2Fe2O3 (s)
4 ATOMS 3 MOLECULES 2 FORMULA UNITS
4 MOLES 3 MOLES MOLES
223.4g g g + =
Convert moles to grams
4mol Fe x 55.85g/1mole = 223.4g
Coefficients = moles
Coefficients = molecules (or formula units for ionic or atoms for elements)

33. Types of Chemical RxN’s
Section 2

34. Types of RxN’s There are millions of reactions.
Can’t remember them all
Fall into several categories.
We will learn 5 types.
Will be able to predict the products.
For some we will be able to predict whether they will happen at all.
Will recognize them by the reactants

35. Types of RxN’s
The classification scheme described in this section provides an introduction to five basic types of reactions:
Synthesis (Combination)
Decomposition
Single-displacement (replacement)
Double-displacement (replacement)
Combustion reactions

36. Synthesis Reactions
In a synthesis reaction, also known as a composition reaction or combination reaction, two or more substances combine to form a new compound.
This type of reaction is represented by the following general equation.
A + X AX
A and X can be elements or compounds.
AX is a compound

37. Synthesis Reactions
2 elements, or compounds combine to make one compound.
Ca +O2 ® CaO
SO3 + H2O ® H2SO4
We can predict the products if they are two elements.
Mg + N2 ®

38. Reactions of Elements with Oxygen
One simple type of synthesis reaction is the combination of an element with oxygen to produce an oxide of the element.
Almost all metals react with oxygen to form oxides.
example: 2Mg(s) + O2(g) 2MgO(s)
Group 2 elements react in a similar manner, forming oxides with the formula MO, where M represents the metal.

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

40. Your Turn III Ca + Cl2 ® Fe + O2 ® iron (II) oxide Al + O2 ®
Remember that the first step is to write the formula
Then balance

41. Decomposition Reactions
In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances. s or compounds.
Decomposition reactions are the opposite of synthesis reactions.
They are represented by the following general equation.
AX A + X
AX is a compound.
A and X can be elements or compounds.

42. Decomposition of Binary Compounds
The decomposition of a substance by an electric current is called electrolysis.
example:
Oxides of the less-active metals, which are located in the lower center of the periodic table, decompose into their elements when heated.
example:

43. Decomposition Reactions
Decomposition of Metal Carbonates
Decomposition of Metal Hydroxides
Decomposition of Metal Chlorates

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

45. Your Turn IV
NiCO3
H2CO3(aq)®

46. Single-Replacement Reactions
In a single-replacement reaction, also known as a displacement reaction, one element replaces a similar element in a compound.
Many single-replacement reactions take place in aqueous solution.
Single-replacement reactions can be represented by the following general equations.
A + BX AX + B or Y + BX BY + X
A, B, X, and Y are elements. AX, BX, and BY are compounds.

47. Single-Replacement Reactions
One element replaces another
Reactants must be an element and a compound.
Products will be a different element and a different compound.
Na + KCl ® K + NaCl
F2 + LiCl ® LiF + Cl2

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

49. Single-Replacement Reactions
Metals replace metals (and hydrogen)
K + AlN ®
Zn + HCl ®
Think of water as HOH
Metals replace one of the H, combine with hydroxide.
Na + HOH ®

50. Activity Series We can tell whether a reaction will happen
Some are more active than other
More active replaces less active
There is a list on page 286
Higher on the list replaces lower.
If the element by itself is higher, it happens, if lower it doesn’t

51. Activity Series H can be replaced in acids by everything higher
Only the first 6 (Li - Na) react with water.
Fe + CuSO4 ®
Pb + KCl ®
Al + HCl ®

52. Activity Series
What does it mean that Au And Ag are on the bottom of the list?
Nonmetals can replace other nonmetals
Limited to F2 , Cl2 , Br2 , I2
The order of activity is that on the table.
Higher replaces lower.
F2 + HCl ®
Br2 + KCl ®

53. Double-Replacement Reactions
In double-replacement reactions, the ions of two compounds exchange places in an aqueous solution to form two new compounds.
One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of the solution, or a molecular compound, usually water.
The other compound is often soluble and remains dissolved in solution.

54. Double-Replacement Reactions
A double-displacement reaction is represented by the following general equation.
AX + BY AY + BX
A, X, B, and Y in the reactants represent ions.
AY and BX represent ionic or molecular compounds.

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

56. Double-Replacement Reactions
The formation of a precipitate occurs when the cations of one reactant combine with the anions of another reactant to form an insoluble or slightly soluble compound.
example:
2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
The precipitate forms as a result of the very strong attractive forces between the Pb2+ cations and the I anions.

57. Double-Replacement Reactions
Two things replace each other.
Reactants must be two ionic compounds or acids.
Usually in aqueous solution
NaOH + FeCl3 ®
The positive ions change place.
NaOH + FeCl3 ® Fe+3 OH- + Na+1Cl-1
NaOH + FeCl3 ® Fe(OH)3 + NaCl

58. Double-Replacement Reactions
Will only happen if one of the products
doesn’t dissolve in water and forms a solid
or is a gas that bubbles out.
or is a covalent compound usually water.

59. Your Turn V assume all of the reactions take place. CaCl2 + NaOH ®
CuCl2 + K2S ®
KOH + Fe(NO3)3 ®
(NH4)2SO4 + BaF2 ®

60. Combustion Reactions
In a combustion reaction, a substance combines with oxygen, releasing a large amount of energy in the form of light and heat.
example: combustion of hydrogen
2H2(g) + O2(g) H2O(g)
example: combustion of propane
C3H8(g) + 5O2(g) CO2(g) + 4H2O(g)

61. Combustion Reactions Combustion
A compound composed of only C H and maybe O is reacted with oxygen
If the combustion is complete, the products will be CO2 and H2O.
If the combustion is incomplete, the products will be CO and H2O.

62. Your Turn VI C4H10 + O2 ® (complete) C4H10 + O2 ® (incomplete)
C6H12O6 + O2 ® (complete)
C8H8 +O2 ® (incomplete)

63. Your Turn VI Part II
Distinguish between complete an incomplete combustion.
Write a balanced equation for the complete combustion of each of these compounds.
a) acetic acid, HC2H3O2 c) glycerol, C3H8O3
b) decane, C10H22 d) sucrose, C12H22O11
Write a balanced equation for the incomplete combustion of each of these compounds.
a) glycerol, C3H8O c) acetic acid, HC2H3O2
b) glucose, C6H12O d) acetylene, C2H2

64. Your Turn VII
Determine the type of reaction and the products and balance.
H2 + O2 ®
H2O ®
Zn + H2SO4 ®
HgO ®
KBr +Cl2 ®
AgNO3 + NaCl ®
Mg(OH)2 + H2SO3 ®

65. Let’s Review
Write out the balanced equation for Copper reacts with chlorine to form copper (II) chloride.
Write out the balanced equation for Zinc reacts with Hydrochloric acid to form Zinc chloride and hydrogen.
Write out the balanced equation for Calcium carbonate reacts with Zinc nitride to form Calcium nitride and Zinc carbonate.

66. Let’s Review Balance the following equations
C7H16 + O2 ---> CO2 + H2O
Na2O2 + H2O ---> NaOH + O2
Al2(SO4)3+Ca(OH)2----> Al(OH)3+CaSO4
NH3 +HCl ----> NH4Cl
Ca3(PO4)2 +SiO2 + C ----> CaSiO3 + CO + P

67. Let’s Review What type of reaction are the following
Rb + S8 ---> Rb2S
NH3 + O2 ---> N2 + H2O
C + SO2 ---> CS2 + CO
C3H11 + O > CO2 + H2O
C5H12 +O > CO + H2O
FeCl3 + NH4OH --->Fe(OH)3 + NH4Cl

68. Let’s Review Balance them Rb + S8 ---> Rb2S
NH3 + O2 ---> N2 + H2O
C + SO2 ---> CS2 + CO
C3H11 + O > CO2 + H2O
C5H12 +O > CO + H2O
FeCl3 + NH4OH --->Fe(OH)3 + NH4Cl

69. Let’s Review Predict the products and balance
Sodium phosphate reacts with Lithium metal.
Butane (C4H10) is completely combusted.
Sodium Chloride reacts with Silver Hydroxide
Aluminum Bromate reacts with Copper
Potassium reacts with Sulfur
Octane (C8H18) is incompletely combusted

70. Let’s Review Predict the products and balance H2 + O2 ® Al2Te3 ®
Zn + H2SO4 ®
HgO ®
KBr +Cl2 ®
AgNO3 + NaCl ®
Mg(OH)2 + H2SO3 ®

71. Let’s Review
Using the table on Pg Predict if these reactions will occur
Li + BaS 
Fe + KCl 
Au + HgS 
Mn + CuS 
Ba + LiS 
Na + KCl 
HCl + Pb 
PbCl2 + H2 