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Types of Reactions

This article discusses the different types of chemical reactions, including synthesis, decomposition, single displacement, double displacement, combustion, and oxidation-reduction (redox) reactions. It also explains how to assign oxidation states and identify oxidizing and reducing agents.

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Types of Reactions

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  1. Types of Reactions

  2. Types of Reactions • Synthesis (Combination) • Decomposition • Single Displacement • Double Displacement • Combustion • Oxidation-Reduction (Redox)

  3. Synthesis • In a synthesis reaction, two substances react to form one new substance. • A + B  AB • A and B can be either an element or a compound • 2 Na + Cl2  2 NaCl • CaO + CO2  CaCO3

  4. Decomposition • In a decomposition reaction, one compound breaks down into two or more simple substances. • AB  A + B • 2 HgO  2 Hg + O2 • 2 KClO3  2 KCl + 3 O2

  5. Single Displacement • In a single displacement reaction, an uncombined element replaces another element in a compound. • Metals replace metals and nonmetals replace nonmetals. • The uncombined element must be more chemically reactive than the element it is replacing in order for the reaction to occur. • A + BC  B + AC

  6. Examples of Single Displacement Reactions • Zn + CuSO4 Cu + ZnSO4 • Cl2 + 2 NaBr  2 NaCl + Br2 • Na + H2O  NaOH + H2

  7. Double Displacement • In a double displacement reaction, the positive and negative ions “change partners” and form two new compounds. • Three types of products may result: a weak/nonelectrolyte, a precipitate, or a gas. • AB + CD  AD + CB

  8. Formation of a Weak/Nonelectrolyte • HCl + NaOH  NaCl + H2O • The above reaction is also referred to as a neutralization reaction. • Neutralization reactions involve the reaction of an acid and base to produce a salt and water.

  9. Formation of a Precipitate • AgNO3 + NaCl  AgCl + NaNO3 • The AgCl is an insoluble salt and will precipitate out of the solution.

  10. Formation of a Gas • 2HCl + CaCO3 CaCl2 + H2CO3 • The H2CO3 decomposes to H2O and CO2. • 2HCl + CaCO3 CaCl2 + H2O + CO2 Another example • MnS + 2HCl  MnCl2 + H2S

  11. Combustion • In a combustion reaction, a hydrocarbon reacts with oxygen to produce carbon dioxide and water. • CxHy + O2 CO2 + H2O

  12. Oxidation-Reduction (Redox) Reactions • Oxidation-reduction reactions are those that involve the transfer of one or more electrons. • All of the previous types of reactions except double displacement are also examples of redox reactions.

  13. Oxidation States • Oxidation states (or oxidation numbers) are a way to keep track of electrons in redox reactions. • Oxidation states are obtained in covalent molecules by arbitrarily assigning the electrons to particular atoms. • Actual charges on ions are written as n+ or n- while oxidation states (not actual charges) are written as +n or -n.

  14. Rules for Assigning Oxidation States • The oxidation state of an atom in an element is 0. • The oxidation state of a monatomic ion is the same as its charge. • In compounds, fluorine is always -1. • Oxygen is usually -2. • Hydrogen is +1 if combined with nonmetals. • The sum of the oxidation states in a neutral compound must be zero. • The sum of the oxidation states in an ion must equal the charge on the ion.

  15. Assigning Oxidation States • Assign the oxidation states to all atoms in the following (Note: Check answers on following slide) CO2 CO SF6 Na2S2O3 NO3- HAsO2 KMnO4 XeOF4 P4O6 Na2C2O4

  16. Answers • C=+4, O=-2 • S=+6, F=-1 • N=+5, O=-2 • K=+1, Mn=+7, O=-2 • P=+3, O=-2 • C=+2, O=-2 • Na=+1, S=+2, O=-2 • H=+1, As=+3, O=-2 • Xe=+6, O=-2, F=-1 • Na=+1, C=+3, O=-2

  17. Characteristics of Oxidation-Reduction Reactions • Redox reactions are characterized by a transfer of electrons • Oxidation is an increase in oxidation state or a loss of electrons. • Reduction is a decrease in oxidation state or a gain of electrons. • OIL RIG • Oxidation is loss; Reduction is gain

  18. Characteristics of Oxidation-Reduction Reactions (continued) • The oxidizing agent is the electron acceptor and consequently undergoes reduction. • The reducing agent is the electron donor and consequently undergoes oxidation.

  19. Identifying Oxidizing and Reducing Agents. • Identify the oxidizing agent, reducing agent, the species oxidized, and the species reduced for each of the following: • 2AgNO3 + Cu  Cu(NO3)2 + 2Ag • 4KClO3(s)  KCl(s) + 3KClO4(s) • 3AgNO3(aq) + K3PO4(aq)  Ag3PO4(s) + 3KNO3(aq)

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