Chapter 8 Chemical Equations and Reactions

Types of Chemical Reactions  Direct Combination: (Synthesis) A + B  AB  Decomposition: AB  A + B  Single Replacement:  Double Replacement:  Combustion: A (metal) + BC  B + AC A (Nonmetal) + BC  C + BA AB + CD  CB + AD AB + CD  AD + CB C ? H ?(g) + O 2(g)  CO 2(g) + H 2 O (g)

Direct Combination (Also called Synthesis or Composition Reactions) Two or more substances combine to form a new compound. A + B  AB  Reaction of elements with oxygen and sulfur  Reactions of metals with Halogens  Synthesis Reactions with Oxides  There are others not covered here! Formation of Water

Direct Combination Two or more substances combine to form a new compound. A + B  AB C + O 2  ________ 2 2 H 2 + O 2  ________ Fe + S  ________ iron(II) sulfide Fe + ___  Fe 2 S 3 iron(III) sulfide Combination reactions with oxygen or sulfur: CO 2 H2OH2O FeS S 2 3

Direct Combination Two or more substances combine to form a new compound. A + B  AB Na + Cl 2  ________2 2 Al + F 2  ________ Combination reactions of metals with halogens: NaCl AlF 3 Ions would be Na + and Cl - Ions would be Al 3+ and F

Direct Combination Two or more substances combine to form a new compound. A + B  AB SO 3 + H 2 O  ________ SO 2 + H 2 O  ________ Combination reactions of nonmetal oxides with water: H 2 SO 4 H 2 SO 3 Form acid with ions H + and SO 4 2- Form acid with ions H + and SO 3 2-

Direct Combination Two or more substances combine to form a new compound. A + B  AB CaO + HOH  ________ Na 2 O + HOH  ________ Combination reactions of metal oxides with water: Ca(OH) 2 NaOH Form base with ions Ca 2+ and OH -1 Form base with ions Na + and OH - 2

Direct Combination Two or more substances combine to form a new compound. A + B  AB Mg (s) + O 2 (g)  MgO (s) 2 2

Balancing Reactions The Law of Conservation of Mass states: Matter is neither created nor destroyed in ordinary chemical reactions. Reactants = Products  Mass is conserved.  Number of atoms is conserved.

Balancing Reactions Formulas CANNOT change. H 2 (g) + O 2 (g)  H 2 O(g) When Balancing Chemical Reactions: Use coefficients to balance the number of atoms. Each side of the arrow has 4 H’s and 2 O’s. 2 2  You MUST know 7 diatomic molecules: H 2, N 2,O 2,F 2 Cl 2 Br 2 I 2

Balancing Reactions To the Website! Link (Chembalancer)Link Link (Sciencegeek.net)Link

Decomposition Reactions A single compound undergoes a reaction that produces two or more simpler substances Decomposition of: Binary compounds (Nitrogen Triiodide) AB  A + B NI 3 (s)  N 2 (g) + I 2 (g) Dark Brown Solid Invisible gas Purple Gas 32 NI 3 (s)

Decomposition Reactions A single compound undergoes a reaction that produces two or more simpler substances Decomposition of: Binary compounds (Lab 10: Copper(II) Chloride) AB  A + B CuCl 2 (aq)  Cu (s) + Cl 2 (g) Blue liquid Reddish solid Bubbles that have distinct odor electrolysis Cu 2+ 2Cl 1-

Oxidation and Reduction (Redox) Electrons are transferred Spontaneous redox rxns can transfer energy Electrons (electricity) Heat Non-spontaneous redox rxns can be made to happen with electricity

Oxidation and Reduction G ain E lectrons = R eduction An old memory device for oxidation and reduction goes like this… LEO says GER L ose E lectrons = O xidation

Decomposition Reactions A single compound undergoes a reaction that produces two or more simpler substances AB  A + B Heat ∆ elect. or Usually occur by adding energy Pt Catalysts are added to speed up a reaction MnO 2 Double arrows indicate the reaction can go both directions

Other Decomposition Reactions A single compound undergoes a reaction that produces two or more simpler substances Decomposition of: Binary compounds 2AlCl 3 (s)  2Al (g) + 3Cl 2 (g) Metal carbonates CaCO 3 (s)  CaO (s) + CO 2 (g) Metal hydroxides Ca(OH) 2 (s)  CaO (s) + H 2 O (g) Metal chlorates 2KClO 3 (s)  2KCl (s) + 3O 2 (g) Oxyacids H 2 CO 3 (aq)  CO 2 (g) + H 2 O ( l ) AB  A + B

Single Replacement Reactions Replacement of:  Metals cations by another metal A (metal) + BC  B + AC Ni + CuCl 2  Cu + NiCl 2  Hydrogen in water by a metal  Hydrogen in an acid by a metal Na + HOH  H 2 + NaOH 2 22 Zn + HCl  H 2 + ZnCl 2 2 Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold Nickel Decreasing activity Copper

Single Replacement Reactions Replacement of: A (metal) + BC  B + AC A (Nonmetal) + BC  C + BA  Halogen anions by more active halogens Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold Fluorine Chlorine Bromine Iodine Decreasing activity F 2 + HCl  Cl 2 + HF22

The Activity Series of the Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold Metals can replace other metals provided that they are above the metal that they are trying to replace. Metals above hydrogen can replace hydrogen in acids. Metals from sodium upward can replace hydrogen in water Zn + CuCl 2  Cu + ZnCl 2 Zn + NaCl  No Reaction Fe + HCl  H 2 + FeCl 3 K + HOH  H 2 + KOH Decreasing activity

The Activity Series of the Halogens Fluorine Chlorine Bromine Iodine Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace. 2NaCl(s) + F 2 (g)  2NaF(s) + Cl 2 (g) MgCl 2 (s) + Br 2 (g)  ???No Reaction ??? Decreasing activity

Double Replacement Reactions The ions of two compounds exchange places in an aqueous solution to form two new compounds. AB + CD  CB + AD One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of solution, or a molecular compound, usually water. AB + CD  AD + CBSame result!

Combustion Reactions A substance combines with oxygen, releasing a large amount of energy in the form of light and heat. P 4 (s) + O 2 (g)  P 4 O 10 (s) (This is also a direct combination reaction) The burning of natural gas, wood, gasoline C 3 H 8 (g) + O 2 (g)  CO 2 (g) + H 2 O(g) C x H y(g) + O 2(g)  CO 2(g) + H 2 O (g) Reactive elements combine with oxygen