Patterns of Chemical Reactivity

1
Patterns of Chemical Reactivity

• Periodic Table predicts the chemical properties
  of compounds of elements.
• Ex All alkali metals react with water
• 2Na(s) 2H2O(l) 2NaOH(aq) H2(g)
• These reactions become more vigorous moving from
  Li to Cs.
• Sodium reacts with water to produce an orange
  flame.
• Potassium and water produces a blue flame and
  enough heat that the hydrogen gas produced
  ignites with a loud pop.

2
Combustion in Air

• Combustion reactions are rapid reactions that
  produce a flame.
• Combustion is the burning of a substance in air.
• Ex Propane combusts to produce carbon dioxide
  and water.
• C3H8(g) 5O2(g) 3CO2(g) 4H2O(l)

3
Combination (Synthesis)

• Two or more substances react to form one product.
• Combination reactions have more reactants than
  products.
• Ex 2Mg(s) O2(g) 2MgO(s)
• Mg closely packed atoms
• O2 dispersed molecules
• MgO lattice of Mg2 and O2- ions (ionic
  compound)

4
Specific Synthesis (Combination) Reactions

• A B ? AB
• Memorize these!
• Metal oxide and water produce a base (OH-)
• X2O H2O ? 2XOH for metals with 1 charge
• XO H2O ? X(OH)2 for metals with 2 charge
• Non-metal oxide and water produce acid (H)
• SO2 H2O ? H2SO3
• CO2 H2O ? H2CO3

5
Synthesis, A B ? AB

• Metal oxides and CO2 produce carbonates
• CaO CO2 ? CaCO3
• Li2O CO2 ? Li2CO3
• Metal oxides and water produce hydroxides
• MgO H2O ? Mg(OH)2
• Na2O H2O ? 2NaOH
• 5. Special reactions
• PCl3 Cl2 ? PCl5
• NH3 BF3 ? H3NBF3

6
Decomposition

• One substance undergoes a reaction to produce two
  or more other substances.
• Decomposition reactions have more products than
  reactants.
• Ex Consider the reaction in a cars airbag
• 2NaN3(s) 2Na(s) 3N2(g)
• Sodium azide decomposes into sodium and nitrogen.

7
Specific Decomposition Reactions

• AB A B
• Binary compounds split up
• Electrolysis is decomposition by electric current
• Example H2O 2H2 O2
• Electrolysis is decomposition by electric current
• Metals with carbonates
• Metal oxide and carbon dioxide are formed
• Example CaCO3 CaO CO2
• Metal hydroxides
• When heated, metal hydroxides decompose to metal
  oxide and water.
• Example Ca(OH)2 CaO H2O

electricity
8
Decomposition Reactions, cont.

• Metal chlorates
• When heated, metal chlorates decompose to metal
  chloride and oxygen.
• Example 2KClO3 2KCl 3O2
• Carbonic acid
• H2CO3 ? CO2 H2O
• 6. Sulfurous acid
• H2SO3 ? SO2 H2O

9
Decomposition Reactions, cont.

• 7. Ammonia(g) production
• NH4OH ? NH3 H2O
• 8. Ammonium carbonate
• (NH4)2CO3 ? 2NH3 H2O CO2
• 9. Hydrogen peroxide
• 2H2O2 ? 2H2O 3O2

10
Single Replacement Reactions

• C AB A CB
• Metal replaces another metal
• Replacing metal must be the more active metal!
• Example 2Al 3Pb(NO3)2 3Pb 2Al(NO3)3
• Metal replaces H in water
• Active metals produce metal hydroxide and water
• Less reactive metals make metal oxide and
  hydrogen gas
• Examples 2Na 2H2O 2NaOH H2
• 3Fe 4H2O Fe3O4 4H2

11
Single Replacement Reactions, cont.

• C AB ?A CB
• Metal replaces H in an acid
• Example Mg 2HCl ? H2 MgCl2
• Halogen replaces another halogen
• Fluorine is most reactive and replaces others.
• Example Cl2 2KBr ? 2KCl Br2
• Br2 2KCl ? No reaction

12
Double Replacement Reactions

• AB CD AD CB
• Precipitate forms (a salt) .
• Example
• 2KI(aq) Pb(NO3)2(aq) PbI2(s) 2KNO3(aq)
• Gas forms.
• FeS(s) 2HCl(aq) H2S (g) 2FeCl2(aq)
• Water forms.
• NaOH(aq) HCl(aq) NaCl (aq) H2O (l)