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AP Chemistry

Unit 4.7

TYPES OF CHEMICAL REACTIONS

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Unit 4.7

Enduring Understanding:

  • A substance that can change into another substance through different processes, and the change itself can be classified by the sort of processes that produced it

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Learning Objective:

  • Identify a reaction as acid-base, oxidation-reduction, or precipitation

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Basic Reaction Types

Composition/Synthesis

Decomposition

Combustion of a hydrocarbon

A + B → AB

AB → A + B

CXHY + O2 → CO2 + H2O

Na + Cl2 → NaCl

KClO3 → KCl + O2

C3H8 + O2 → CO2 + H2O

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Basic Reaction Types

  • Double replacement reactions include acid/base neutralization and precipitation reactions
  • All of these reactions can be considered RedOx (reduction/oxidation) reactions except the double replacement reactions

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Single (ionic) replacement

Double (ionic) replacement

Combustion of a metal

A + BC → AC + B

AB + CD → AD + CB

M + O2 → MXOY

Mg + HCl → MgCl2 + H2

LiCl + AgNO3 → LiNO3 + AgCl

Mg + O2 → MgO

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Acid-Base Reactions

  • Involve the transfer of one or more protons between chemical species
  • Acids: protons donors
  • Bases: proton acceptors
  • Protons: hydrogen ions
    • Water + hydrogen ion = hydronium (H3O)
    • Protons = hydrogen ion = hydronium
  • Conjugate acid: what the base becomes when it gains a proton
  • Conjugate base: what the acid becomes when it loses a proton
  • Amphoteric: substances that can act as an acid and a base

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Acid-Base Reactions

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Acid-Base Reactions

  • Acids and bases are described as being strong or weak
  • Strong means that the substance will completely separate into ions
  • Weak means that the substance will only partially separate into its ions
  • Strong/weak ≠ concentrated/dilute

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Oxidation-Reduction Reactions

  • Involve the transfer of one or more electrons between chemical species, as indicated by changes in oxidation numbers
  • Combustion is a subclass of redox reactions
  • LEO says GER; OIL RIG
    • Oxidation: loss of electrons
    • Reduction: gain of electrons
  • The species that is oxidized is the reducing agent
  • The species that is reduced is the oxidizing agent

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Oxidation-Reduction Reactions

  • Involve the transfer of one or more electrons between chemical species, as indicated by changes in oxidation numbers
  • Combustion is a subclass of redox reactions
  • LEO says GER; OIL RIG
    • Oxidation: loss of electrons
    • Reduction: gain of electrons
  • The species that is oxidized is the reducing agent
  • The species that is reduced is the oxidizing agent

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Cu2+ (aq) + 2NO3- (aq) + 2Na (s) → Cu (s) + 2Na+ (aq) + 2NO3-(aq)

Cu(NO3)2 (aq) + 2Na (s) → Cu (s) + 2NaNO3 (aq)

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Oxidation-Reduction Reactions

  • Oxidation numbers: assigned to each atom in the reaction (reactants and products) that shows their apparent charge
    • Apparent charge: the charge the atom would have if it was an ion
  • If the oxidation number increases (becomes more positive) from reactants to products then electrons have been lost so oxidation has occurred
  • If the oxidation number decreases (becomes more negative) from reactants to products then electrons have been gained so reduction has occurred

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Oxidation-Reduction Reactions

  • Oxidation numbers: assigned to each atom in the reaction (reactants and products) that shows their apparent charge
    • Apparent charge: the charge the atom would have if it was an ion
  • If the oxidation number increases (becomes more positive) from reactants to products then electrons have been lost so oxidation has occurred
  • If the oxidation number decreases (becomes more negative) from reactants to products then electrons have been gained so reduction has occurred

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Precipitation Reactions

  • Involve mixing ions in aqueous solution to produce an insoluble or sparingly soluble ionic compound.
  • A type of double replacement reaction
  • The solid portion of the reaction is called the precipitate
    • Can be predicted using solubility rules
    • SNAP = soluble
  • Often use net ionic equations to identify spectator ions
  • General format:
    • AB (aq) + CD (aq) → AD (s) + CB (aq)

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Practice: I Do

  1. Sodium metal, Na, reacts with a solution of sulfuric acid, H2SO4, to form hydrogen gas, H2, and a solution of sodium sulfate, Na2SO4
    1. Write a balanced equation
    2. Assign oxidation numbers
    3. Use the oxidation numbers to determine which substance was oxidized and which was reduced

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Practice: I Do

  • Sodium metal, Na, reacts with a solution of sulfuric acid, H2SO4, to form hydrogen gas, H2, and a solution of sodium sulfate, Na2SO4
    • Write a balanced equation

2Na (s) + H2SO4 (aq) → H2 (g) + Na2SO4 (aq)

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Practice: I Do

  • Sodium metal, Na, reacts with a solution of sulfuric acid, H2SO4, to form hydrogen gas, H2, and a solution of sodium sulfate, Na2SO4
    • Assign oxidation numbers

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2Na (s) + H2SO4 (aq) → H2 (g) + Na2SO4 (aq)

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+1

+6

-2

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+1

+6

-2

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Practice: I Do

  • Sodium metal, Na, reacts with a solution of sulfuric acid, H2SO4, to form hydrogen gas, H2, and a solution of sodium sulfate, Na2SO4
    • Use the oxidation numbers to determine which substances were oxidized/reduced

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2Na (s) + H2SO4 (aq) → H2 (g) + Na2SO4 (aq)

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0

+1

+6

-2

0

+1

+6

-2

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Practice: I Do

  • Sodium metal, Na, reacts with a solution of sulfuric acid, H2SO4, to form hydrogen gas, H2, and a solution of sodium sulfate, Na2SO4
    • Use the oxidation numbers to determine which substances were oxidized/reduced

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2Na (s) + H2SO4 (aq) → H2 (g) + Na2SO4 (aq)

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0

+1

+6

-2

0

+1

+6

-2