1 / 16

Redox Reactions

Redox Reactions. Chapter 20. Section 20.1. Oxidation And Reduction. Redox Reactions. A chemical rxn in which electrons are transferred from one atom to another is called an oxidation-reduction reaction , or redox rxn .

alton
Download Presentation

Redox Reactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Redox Reactions Chapter 20

  2. Section 20.1 Oxidation And Reduction

  3. Redox Reactions • A chemical rxn in which electrons are transferred from one atom to another is called an oxidation-reduction reaction, or redox rxn. • In a redox reaction, the loss of electrons from atoms of a substance is called oxidation. • The gain of electrons is called reduction.

  4. Changes in Oxidation Number • You already learned that the oxidation number of an atom is equal to the number of electrons gained or lost in an ionic compound. • Oxidation increases an atom’s oxidation number; reduction decreases the oxidation number.

  5. Complementary Processes • Oxidation and reduction are complementary processes that always occur together. • The substance that is reduced in a redox reaction is the oxidizing agent. • The substance that is oxidized in a redox rxn is the reducing agent.

  6. Example • Redox rxn are not limited to reactions in which atoms change to ions or vice versa. • For example in the rxn, identify the oxidizing and reducing agent H2 (g) + Cl2 (g)  2HCl (g)

  7. Practice Problems • Identify what is oxidized and what is reduced. Also identify the oxidizing agent and the reducing agent. • Zn + Ni2+ Ni + Zn2+ • 2I- + Br2  I2 + 2Br- • 2NO  N2 + O2 • 2H2 + S2  2H2S

  8. Determining Oxidation Numbers • Use these rules to determine the oxidation numbers in redox reactions. • The oxidation number of an uncombined atom is zero. • The oxidation number of a monatomic ion is equal to the charge on the ion. • The oxidation number of the more electronegative atom in a molecule or complex ion is the same as the charge it would have if it were an ion. • The most oxidation number of oxygen in compounds is always -2, except in peroxides, where it is -1. When bonded to fluorine the oxidation number of oxygen is 2+.

  9. Example • Determine the oxidation number of each element in the following compound and ion. a. SrCO3 b. Cr2O72-

  10. Practice Problems • Determine the oxidation number of the boldface element in each of these compounds. • Li2SiO3 • Al4C3 • CaH2 • BeSeO4 • K2GeF6 • Al(ClO3)3 • Determine the oxidation number of the boldface element in each of these ions. • PO43- • Hg22+ • HSO4- • PtCl62- • PuO2+ • TeO32-

  11. Reactions as RedoxRxn • Not all chemical rxns are redox rxns. • Most double-displacement rxns are not redox rxns, because there is not transfer of electrons between atoms. • Combustion and single-replacement rxns are always redox rxns. • Many synthesis and decomposition rxns are redox rxns as well.

  12. Section 20.3 Half-Reactions

  13. Balancing Redox Reaction • When balancing redox rxns in addition to balancing the # of each atom, the number of electrons gained or lost must also be balanced. • The method used is balancing half-reactions. • A half-reaction shows the oxidation half of the rxn, and the reduction half of the rxn in each half-rxn. • One half-rxn shows the oxidation and the other shows the reduction.

  14. Balancing Half-Reactions • The steps to balance a redox half-reaction are as follows: • Write the net ionic equation for the rxn, omitting spectator ions. • Write the oxidation and reduction half-reactions for the net ionic equation. • Balance the atoms and charges in each half-reaction. • Adjust the coefficients so that the # of electrons lost in the oxidation equals the # of electrons gained in reduction. • Add the balanced half-reactions and return spectator ions.

  15. Example • Use the half-reaction method to balance this equation. K2Cr2O7 (aq) + HCl (aq)  CrCl3 (aq) + KCl (aq) + Cl2 (g)

  16. Practice • Use the half-reaction method to balance. • I2 (s) + H2SO3 (aq)  I- (aq) + HSO4- (aq) • Fe2+ (aq) + MnO4- (aq)  Fe3+ (aq) + Mn2+ (aq) • Zn (s) + Cr2O72- (aq)  Zn2+ (aq) + Cr3+ (aq) • IO3- (aq) + I- (aq)  I2 (s)

More Related