ElectroChem

ElectroChem - 1 Electrochemistry Electrochem Slide 2...

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Unformatted text preview: 1 Electrochemistry Electrochem Slide 2 Electrochemistry The area of chemistry that studies the use of chemical reactions to produce electricity and the use of electricity to produce chemical change Study of the transfer of electrons and redox chemistry Oxidation : the loss of electrons; causes that species to have an increase in oxidation number. Reduction : the gain of electrons; causes that species to have an decrease in oxidation number. Oxidation Number (or Oxidation State ): the imaginary charge an atom would have if shared electrons were equally divided between identical atoms bound to one another, or, for different atoms, if electrons in a bond were all assigned to the partner with the higher electronegativity 2 Electrochem Slide 3 Oxidation Number ( ON ) Determination 1. The ON of an atom as an element is zero: Na(s), C(gr), H 2 (g), I 2 (s); 2. For a monatomic ion, its charge is its ON; 3. F is always 1; 4. Group I elements are always +1; Group II elements are always +2; 5. Oxygen is usually assigned an ON of 2; the only exception is for peroxides (species where you have OO bonds) where oxygen has an ON of 1; 6. Hydrogen is +1 when combined with non-metals and 1 when combined with metals (hydrides); 7. The sum of the oxidation states of all atoms in a compound must equal the charge on the compound or ion of interest; 8. Non-integer oxidation states DO exist (Fe 3 O 4 ) Electrochem Slide 4 Oxidation Number ( ON ) Determination A compound (ionic or covalent) is neutral and has a charge of zero. An ion WILL have a TOTAL charge; The sum of all the oxidation states in a compound must equal the overall charge on the ion or molecule. Set up and solve for the unknown algebraically; For Fe 2 O 3 : For Cr 2 O 7 2 : # irons ( ) ! charge of iron ( ) [ ] + # oxygens ( ) ! charge of oxygen ( ) [ ] = charge of Fe 2 O 3 2 x ( ) [ ] + 3 " 2 ( ) ( ) [ ] = 0; solve to get x = +3 # of chromiums ( ) ! charge of iron ( ) " # $ % + # oxygens ( ) ! charge of oxygen ( ) " # $ % = charge of Cr 2 O 7 2 2 x ( ) " # $ % + 7 & 2 ( ) ( ) " # $ % = 2; solve to get x = +6 2 Electrochem Slide 3 Oxidation Number ( ON ) Determination 1. The ON of an atom as an element is zero: Na(s), C(gr), H 2 (g), I 2 (s); 2. For a monatomic ion, its charge is its ON; 3. F is always 1; 4. Group I elements are always +1; Group II elements are always +2; 5. Oxygen is usually assigned an ON of 2; the only exception is for peroxides (species where you have OO bonds) where oxygen has an ON of 1; 6. Hydrogen is +1 when combined with non-metals and 1 when combined with metals (hydrides); 7. The sum of the oxidation states of all atoms in a compound must equal the charge on the compound or ion of interest; 8. Non-integer oxidation states DO exist (Fe 3 O 4 ) Electrochem Slide 4 Oxidation Number ( ON ) Determination A compound (ionic or covalent) is neutral and has a charge of zero....
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This note was uploaded on 04/06/2008 for the course CHEM 6 taught by Professor Bernoililes during the Spring '08 term at UCSD.

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ElectroChem - 1 Electrochemistry Electrochem Slide 2...

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