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Electrochemistry

Electrochemistry. Electrochemistry. Interconversion of electrical and chemical energy. Electrochemical cells. 1. Voltaic cell – spontaneous reaction generates electricity. Dry cells. Alkaline battery. Lead acid battery.

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Electrochemistry

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  1. Electrochemistry

  2. Electrochemistry • Interconversion of electrical and chemical energy

  3. Electrochemical cells 1. Voltaic cell – spontaneous reaction generates electricity

  4. Dry cells

  5. Alkaline battery

  6. Lead acid battery

  7. 2. Electrolytic cell – electrical energy used to bring about a nonspontaneous reaction

  8. Anode - Cathode

  9. Electroplating

  10. Redox Reactions(oxidation – reduction)

  11. Oxidation • Loss of electrons or gain of oxygen

  12. Reduction • Gain of electrons or loss of oxygen

  13. Redox reactions

  14. Redox reactions The reaction between hydrogen and fluorine(hydrogen is oxidized and fluorine is reduced) • H2 + F2 → 2 HF half-reactions: • oxidation reaction: H2→ 2 H+ + 2 e⁻ • reduction reaction: F2+ 2 e⁻ → 2 F−

  15. Redox The reaction between iron and copper(II) sulfate solution: • Fe + CuSO4 → FeSO4 + Cu • As two half-equations, it is seen that the iron is oxidized: Fe → Fe2+ + 2 e⁻ • And the copper is reduced: Cu2+ + 2 e⁻ → Cu

  16. Oxidation numbers • Oxidation numbers are used to keep track of how many electrons are lost or gained by each atom

  17. Rules • The convention is that the cation is written first in a formula, followed by the anion. For example, in NaH, the H is H-; in HCl, the H is H+. • The oxidation number of a free element is always 0. The atoms in He and N2, for example, have oxidation numbers of 0. • The oxidation number of a monatomic ion equals the charge of the ion. For example, the oxidation number of Na+ is +1; the oxidation number of N3- is -3. • The usual oxidation number of hydrogen is +1. The oxidation number of hydrogen is -1 in compounds containing elements that are less electronegative than hydrogen, as in CaH2.

  18. 5. The oxidation number of oxygen in compounds is usually -2. 6. The oxidation number of a Group 1 element in a compound is +1. 7. The oxidation number of a Group 2 element in a compound is +2. 8. The oxidation number of a Group 17 element in a compound is -1, except when that element is combined with one having a higher electronegativity. 9. The sum of the oxidation numbers of all of the atoms in a neutral compound is 0. 10. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion. For example, the sum of the oxidation numbers for SO42- is -2.

  19. examples SO2 • S +4 O -2 CO32- • C ? O -2 • Therefore C = +4 • (+4 + (3x(-2)) = -2

  20. Na2SO4 • Na +1 (rule 1) • O -2 • S +6

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