1. Chapter 8 – Chemical Equations and Reactions
Honors Chemistry, Chapter 8
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2. Honors Chemistry, Chapter 8
Chemical Equations
A chemical equation represents, with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction.
Reactants – Starting substances on the left side of the equation
Products – Final substances on the right side of the equation
Obeys the Law of Conservation of Mass
Honors Chemistry, Chapter 8
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3. Indications of a Chemical Reaction
Evolution of heat and light. (Examples: Decomposition of ammonium dichromate, burning of methane.)
Production of a gas. (Example: Carbon dioxide released when baking soda and vinegar react.)
Honors Chemistry, Chapter 8
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4. Indications of a Chemical Reaction
Formation of a precipitate. (Example: Reaction of ammonium sulfide and cadmium nitrate  Yellow ppt.)
Color Change. (Example: When iron and water react the iron changes from metallic color to red/brown.)
Honors Chemistry, Chapter 8
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5. Characteristics of Chemical Equations
The equation must represent the known facts (all reactants and products must be identified by chemical analysis.)
The equation must contain the correct formulas for the reactants and products.
The law of conservation of mass must be satisfied. (Coefficients added as necessary. Coefficient: a small whole number in front of a formula in a chemical equation.)
Honors Chemistry, Chapter 8
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6. Elements That Normally Appear as Diatomic or Polyatomic Molecules
Symbol
Molecular Formula
Physical State
Hydrogen H H2
Gas
Nitrogen N N2
Oxygen O O2
Fluorine F F2
Chlorine Cl
Cl2
Honors Chemistry, Chapter 8
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7. Elements That Normally Appear as Diatomic or Polyatomic Molecules
Symbol
Molecular Formula
Physical State
Bromine Br
Br2
Liquid
Iodine I I2
Solid
Sulfur S S8
Phosphorous P P4
Honors Chemistry, Chapter 8
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8. Word Equations
Word equation: An equation in which the reactants and products of a chemical reaction are represented by words.
Methane + oxygen  carbon dioxide + Water
Arrow ( ) is read as: “react to yield”, “yield”, “produce”, or “form”
Honors Chemistry, Chapter 8
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9. Formula Equations
Formula equation: An equation which represents the reactants and products of a chemical reaction by their symbols or formulas.
CH4(g) + O2(g)  CO2 (g) + H2O(g) (not balanced)
CH4(g) + O2(g)  CO2 (g) + 2H2O(g) (partially balanced)
CH4(g) + 2O2(g)  CO2 (g) + 2H2O(g) (balanced)
Honors Chemistry, Chapter 8
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10. Symbols Used in Chemical Equations
Explanation
Yields; indicates result of a reaction
Indicates a reversible reaction
(s)
Reactant or product in the solid state
Precipitate
(l)
Reactant or product in the liquid state
(aq)
Reactant or product in aqueous solution
(g)
Reactant or product in the gaseous state
Honors Chemistry, Chapter 8
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11. Symbols Used in Chemical Equations
Explanation
Product in the gaseous state D
Reactants are heated (D or heat)
2 atm
Reaction at 2 atmospheres pressure
pressure
Reaction at elevated pressure
0oC
Reaction at 0oC
MnO2
Reaction in the presence of a catalyst
Honors Chemistry, Chapter 8
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12. Reaction Symbol Definitions
Catalyst: A catalyst is a substance that changes the rate of a chemical reaction but can be recovered unchanged.
Reversable Reaction: A chemical reaction in which the products re-form the original reactants.
Honors Chemistry, Chapter 8
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13. Practice Writing Formulas
Barium Acetate Ammonium Sulfate
Aluminum Carbonate Iron (III) Chromate
Nickel (II) Hydroxide Copper (II) Nitrate
Rubidium Chloride Lithium Permanganate
Strontium Peroxide Calcium Phosphate
Mercury (I) Sulfate Magnesium Bromide
Zinc Thiosulfate Tin (IV) Chlorate
Honors Chemistry, Chapter 8
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14. Honors Chemistry, Chapter 8
Example Reactions
3Fe(s) + 4 H2O(g) Fe3O4 + 4 H2(g)
2HgO(s) Hg(l) + O2(g)
C2H4(g) + H2(g) C2H6(g) D
Pressure Pt
Honors Chemistry, Chapter 8
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15. Significance of a Chemical Equation
The coefficients of a chemical reaction indicate relative, not absolute amounts of reactants and products.
H2(g) + Cl2(g)  2HCl(g)
In other words:
1 molecule H2 : 1 molecule Cl2 : 2 molecules HCl Or
1 mole H2 : 1 mole Cl2 : 2 mole HCl
Honors Chemistry, Chapter 8
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16. Significance of a Chemical Equation
The relative masses of the reactants and products of a chemical reaction can be determined from the reaction’s coefficients.
1 mol H2 x 2.02 g H2/mol H2 = 2.02 g H2
1 mol Cl2 x g Cl2/mol Cl2 = g Cl2
2 mol HCl x g HCl/mol HCl = g HCl
Honors Chemistry, Chapter 8
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17. Significance of a Chemical Equation
The reverse for a chemical reaction has the same relative amounts of substances as the forward reaction.
Honors Chemistry, Chapter 8
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18. Balancing Chemical Equations
Identify the names of the reactants and the products and write the word equation.
Water  hydrogen + oxygen
Write a formula equation by substituting correct formulas for the names of the reactants and the products.
H2O(l)  H2(g) + O2(g) (not balanced)
Honors Chemistry, Chapter 8
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19. Balancing Chemical Equations
Balance the equation according to the law of conservation of mass
Balance different types of atoms one at a time.
First balance the atoms of elements that are combined and that appear only once on each side of the equation.
Balance polyatomic ions that appear on both sides of the equation as single units.
Balance H atoms and O atoms after all other elements are balanced.
2H2O(l)  H2(g) + O2(g) (Partially balanced)
2H2O(l)  2H2(g) + O2(g) (balanced)
Honors Chemistry, Chapter 8
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20. Balancing Chemical Equations
Count atoms to be sure the equation is balanced.
2H2O(l)  2H2(g) + O2(g) (balanced)
(4H + 2O) = (4H) (2O)
Honors Chemistry, Chapter 8
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21. Honors Chemistry, Chapter 8
When Balancing . . .
Always write the correct formulas for both the reactants and the products
Never try to balance an equation by changing subscripts(!)
Honors Chemistry, Chapter 8
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22. Honors Chemistry, Chapter 8
Balancing Exercise #1
Using the four steps, write a balanced chemical equation for the reaction between zinc and aqueous hydrochloric acid which produces zinc chloride and hydrogen gas.
Honors Chemistry, Chapter 8
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23. Honors Chemistry, Chapter 8
Exercise #1 - Solution
zinc + hydrochloric acid  zinc chloride + Hydrogen
Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g)
Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
(1 Zn)+(2H + 2Cl) = (1Zn+2Cl) + (2H)
Honors Chemistry, Chapter 8
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24. Honors Chemistry, Chapter 8
Balancing Exercise #2
Using the four steps, write a balanced chemical equation for the reaction between aluminum carbide (Al4C3) and water which produces methane gas (CH4) and aluminum hydroxide.
Honors Chemistry, Chapter 8
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25. Honors Chemistry, Chapter 8
Exercise #2 - Solution
aluminum carbide + water  methane + aluminum hydroxide
Al4C3(s) + H2O(l)  CH4(g) + Al(OH)3(s)
Al4C3(s)+12H2O(l)3CH4(g)+4Al(OH)3(s)
(4Al+3C)+(24H+12O)
= (3C+12H) + (4Al+12O+12H)
Honors Chemistry, Chapter 8
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26. Honors Chemistry, Chapter 8
Balancing Exercise #3
Using the four steps, write a balanced chemical equation for the reaction between calcium carbide (CaC2) and water which produces ethyne gas (HCCH) (also known as acetylene) and calcium hydroxide.
Honors Chemistry, Chapter 8
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27. Honors Chemistry, Chapter 8
Exercise #3 - Solution
calcium carbide + water  ethyne + calcium hydroxide
CaC2(s)+H2O(l)  HCCH(g)+Ca(OH)2(s)
CaC2(s)+2H2O(l)  HCCH(g)+Ca(OH)2(s)
(1Ca+2C)+(4H+2O)
= (2H + 2C) + (1Ca+2O+2H)
Honors Chemistry, Chapter 8
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28. Chapter 8, Section 1 Review
List four observations that indicate that a chemical reaction has taken place.
List three requirements for a correctly written chemical equation.
Write a word equation and a formula equation for a given chemical reaction.
Balance a formula equation by inspection.
Honors Chemistry, Chapter 8
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29. Broad Types of Chemical Reactions
Synthesis: A + X AX
Decomposition: AX  A + X
Single-Replacement: A + BX  AX + B or Y + BX  BY + X
Double-Replacement: AX + BY AY + BX
Combustion: 2A + O2  2AO
(coefficients and subscripts may vary)
Honors Chemistry, Chapter 8
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30. Honors Chemistry, Chapter 8
Synthesis Reactions
In a synthesis reaction, also known as a composition reaction, two or more substances combine to form a new compound.
A + X AX
Three Types
Elements + Oxygen or Sulfur
Metals with Halogens
Reactions with Oxides
Honors Chemistry, Chapter 8
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31. Reactions of Elements with Oxygen or Sulfur
Mg(s) + O2(g)  ? Mg(s) + O2(g) 2MgO(s)
Rb(s) + S8(s)  ? Rb(s)+S8(s) 8Rb2S(s)
Fe(s) + O2(g)  ? Fe(s) + O2  2FeO 4Fe(s) + 3O2  2Fe2O3
Honors Chemistry, Chapter 8
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32. Reactions of Elements with Oxygen or Sulfur
C(s) + O2(g)  ? C(s) + O2(g)  CO2(g) 2C(s) + O2(g) 2CO(g)
S8(s) + O2  ? S8(s) + 8O2  8 SO2(g)
H2(g) + O2(g)  ? H2(g) + O2(g) 2H2O(g)
Honors Chemistry, Chapter 8
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33. Reactions of Metals with Halogens
Na(s) + Cl2(g)  ? Na(s) + Cl2(g)  2NaCl(s)
K(s) + I2(s)  ? K(s) + I2(s)  2KI(s)
Mg(s) + F2(g)  ? Mg(s) + F2(g)  MgF2(s)
Sr(s) + Br2(l)  ? Sr(s) + Br2(l)  SrBr2(s)
Honors Chemistry, Chapter 8
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34. Reactions of Metals with Halogens
Na(s) + F2(g)  ? Na(s) + F2(g)  2NaF(s)
Co(s) + F2(g)  ? Co(s) + 3F2(g)  2CoF3(s)
U(s) + F2(g)  ? (Hint: Uranium (VI)) U(s) + 3F2(g)  UF6(g)
Honors Chemistry, Chapter 8
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35. Synthesis Reactions with Oxides
CaO(s) + H2O(l)  ? CaO(s)+H2O(l)Ca(OH)2(s)
SO2(g) + H2O(l)  ? SO2(g)+H2O(l)  H2SO3(aq)
H2SO3(aq) + O2(g)  ? H2SO3(aq) + O2(g)  2H2SO4(aq)
CaO(s) + SO2(g)  ? CaO(s)+ SO2(g)  CaSO3(s)
Honors Chemistry, Chapter 8
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36. Decomposition Reactions
In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances.
AX A + X
Five Types
Decomposition of Binary Compounds
Decomposition of Metal Carbonates
Decomposition of Metal Hydroxides
Decomposition of Metal Chlorates
Decomposition of Acids
Honors Chemistry, Chapter 8
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37. Decomposition of Binary Compounds
H2O(l) electricity ? H2O(l) electricity 2H2(g) + O2(g) (electrolysis)
HgO(s) D ? HgO(s) D 2 Hg(l) + O2(g) (thermolysis)
Honors Chemistry, Chapter 8
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38. Honors Chemistry, Chapter 8
Decompostion of Metal Carbonates
CaCO3(s) D ? CaCO3 D CaO(s) + CO2(g)
Decomposition of Metal Hydroxides
Ca(OH)2(s) D ? Ca(OH)2(s) D CaO(s)+H2O(g)
Honors Chemistry, Chapter 8
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39. Honors Chemistry, Chapter 8
Decompostion of Metal Chlorates
KClO3(s) D ? KClO3(s) D 2KCl(s)+3O2(g)
Decomposition of Acids
H2CO3(aq)  ? H2CO3(aq)  CO2(g)+H2O(l)
H2SO4(aq) D ? H2SO4(aq) D SO3(g)+H2O(l)
(Sulfurous Acid  ?)
Honors Chemistry, Chapter 8
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40. Single-Replacement Reactions
In a single-replacement reaction, also known as a displacement reaction, one element replaces a similar element in a compound.
A + BX AX + B or
Y + BX  BY + X
Four Types
Replacement of a Metal by Another Metal
Replacement of H2 in Water by a Metal
Replacement of H2 in an Acid by a Metal
Replacement of Halogens
Honors Chemistry, Chapter 8
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41. Honors Chemistry, Chapter 8
Replacement of a Metal with another Metal
Al(s) + Pb(NO3)2(aq)  ? 2Al(s)+3Pb(NO3)2(aq)3Pb(s)+2Al(NO3)3
Replacement of H2 in Water by a Metal
Na(s) + H2O(l)  ? Na(s)+ 2H2O(l)  2NaOH(aq) + H2(g)
Fe(s) + H2O(g)  ? Fe(s)+ 4H2O(g)  Fe3O4(s)+ 4H2(g)
(Oxidation State of Fe?)
Honors Chemistry, Chapter 8
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42. Honors Chemistry, Chapter 8
Replacement of H2 in an Acid by a Metal
Mg(s) + HCl(aq)  ?
Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
Replacement of Halogens
Cl2(g) + 2KBr(aq)  2KCl(aq) + Br2(l)
F2(g) + 2NaCl(aq)  2NaF(aq) + Cl2(g)
Br2(l) + KCl(aq)  no reaction
Honors Chemistry, Chapter 8
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43. Double-Replacement Reactions
In double-replacement reactions, the ions of two compounds exchange places to make two new compounds.
AX + BY AY + BX
Three Types
Formation of a Precipitate
Formation of a Gas
Formation of Water
Honors Chemistry, Chapter 8
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44. Honors Chemistry, Chapter 8
Formation of a Precipitate
KI(aq) + Pb(NO3)2(aq)  ?
2KI(aq)+Pb(NO3)2(aq)PbI2(s)+ 2KNO3(aq)
Formation of a Gas
FeS(s) + 2HCl(aq)  H2S(g) + FeCl2(aq)
Formation of Water (acid-base reactions)
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
Honors Chemistry, Chapter 8
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45. Honors Chemistry, Chapter 8
Combustion Reactions
In a combustion reaction, a substance combines with oxygen, releasing a large amount of energy in the form of light and heat.
2H2(g) + O2(g)  2H2O(g)
C3H8(g) + 5O2  3CO2(g) + 4H2O(g)
Honors Chemistry, Chapter 8
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46. Chapter 8, Section 2 Review
Define and give general equations for:
Synthesis reactions
Decomposition reactions
Single-replacement reactions
Double-replacement reactions
Combustion reactions
Classify a reaction into one of the five categories above.
Honors Chemistry, Chapter 8
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47. Chapter 8, Section 2 Review continued
List three types of synthesis reactions and five types of decomposition reactions.
List four types of single replacement reactions and three types of double replacement reactions.
Predict the products of simple reactions given the reactants.
Honors Chemistry, Chapter 8
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48. Honors Chemistry, Chapter 8
Activity Series
An Activity series is a list of elements organized according to the ease with which the elements undergo certain chemical reactions.
Each element in the series will replace all elements below it in the series in a single-replacement reaction.
Honors Chemistry, Chapter 8
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49. Activity Series of Metals
Rx with water
Rx with steam
Rx with acids
Rx with oxygen
Unreactive Li Rb K Ba Sr Ca Na Mg Al Mn Zn Cr Fe Cd Co Ni Sn Pb H2 Sb Bi Cu Hg Ag Pt Au
Honors Chemistry, Chapter 8
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50. Activity Series of Halogens
Fluorine
Chlorine
Bromine
Iodine
Honors Chemistry, Chapter 8
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51. Chapter 8, Section 3 Review
Explain the significance of an activity series.
Use an activity series to predict whether a given reaction will occur and what the products will be.
Honors Chemistry, Chapter 8
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