8-2: Types of Chemical Reactions

1. 8-2: Types of Chemical Reactions

2. Classifying Chemical Changes • The products of a chemical reaction may often be predicted by applying known facts about common reaction types • Five general types of reactions: • Single displacement • Double displacement • Decomposition • Synthesis • Combustion

3. Single Displacement • (aka single replacement) • One element displaces another element in a compound • Metal replaces metal (+) • Nonmetal replaces nonmetal (-) • General form: • element + compound  element + compound A + BC  B + AC

4. General types of single displacement reactions: • An active metal will replace the metallic ion in a compound of a less active metal. • Ex: Fe + Cu(NO3)2  Fe(NO3)2+ Cu • Some active metals such as sodium and calcium will react with water to give a metallic hydroxide and hydrogen gas. • Ex: Ca + 2H2O  Ca(OH)2+ H2 • Active metals such as zinc, iron, and aluminum will displace the hydrogen in acids to give a salt and hydrogen gas. • Ex: Zn + 2HCl  ZnCl2+ H2 • An active nonmetal will displace a less active nonmetal. • Ex: Cl2+ 2NaBr  2NaCl + Br2

5. Double Displacement • (aka double replacement) • Ions in two compounds “change partners” • Cation of one compound combines with the anion of the other compound • General form: • compound + compound  compound + compound AB + CD  AD + CB

6. General types of double displacement reactions: • A reaction between an acid and a base yields a salt and water. Such a reaction is a neutralization reaction. • Ex: 2KOH+ H2SO4 K2SO4+ 2H2O • Reaction of a salt with an acid forms a salt of the acid and a second acid that is volatile. • Ex: 2KNO3+ H2SO4 K2SO4 + 3HNO4 • Reactions of some soluble salts produce an insoluble salt and a soluble salt. • Ex: AgNO3+ NaCl  AgCl+ NaNO3

7. Decomposition • A compound breaks down into 2 or more simpler substances • Only one reactant • General form: • compound  two or more substances AB  A + B

8. General types of decomposition reactions: • When some acids are heated, they decompose to form water and an acidic oxide. • Ex: H2CO3 CO2+ H2O • When some metallic hydroxides are heated, they decompose to form metallic oxide and water. • Ex: Ca(OH)2 CaO+ H2O • When some metallic carbonates are heated, they decompose to form a metallic oxide and carbon dioxide. • Ex: Li2CO3 Li2O + CO2 • Most metallic oxides are stable, but a few decompose when heated. • Ex: 2HgO  2Hg + O2 • Some compounds cannot be decomposed by heat, but can be decomposed into their elements by electricity. • Ex: 2NaCl  2Na+ Cl2

9. Synthesis • The combination of 2 or more substances to form a compound • Only one product • General form: • element or compound + element or compound  compound A + B  AB

10. General types of synthesis reactions: • Two or more elements combine to form a compound. • Ex: Fe + S  FeS • An acid anhydride, nonmetallic oxide, combines with water to give an acid. • Ex: SO2+ H2O  H2SO3 • A basic anhydride, metallic oxide, combines with water to form a base. • Ex: Na2O + H2O  2NaOH • A basic oxide combines with a nonmetallic oxide to form a salt. • Ex: CO2+ Na2O  Na2CO3

11. Combustion • Contains oxygen • Hydrocarbons form CO2 + H2O • Ex: The combustion of hydrogen2H2+ O2 2H2O • Ex: The burning of propaneC3H8+ 5O2 3CO2+ 4H2O