LECTURE 26 Electrochemistry

LECTURE 26 Electrochemistry - SUMMARY FROM LAST CLASS...

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Dr. P. Lucas U of A MSE 110 Optical devices SUMMARY FROM LAST CLASS LASER: Light Amplification by Stimulated Emission of Radiation. Stimulated emission: a photon stimulates an electronic transition in an excited active species which generates a second identical photon. The active species is enclosed between two mirrors in the laser cavity . The active species is pumped into a higher electronic state with a flash of light or an electric discharge to create a population of excited atoms A photon reflected back and forth between the mirrors induces stimulated emissions and generates an amplified coherent beam. The length of the laser cavity must be equal to an integral number of wavelength emitted by the active species in order to prevent destructive interferences. L = n λ A laser beam is therefore monochromatic , coherent and colinear . In a solid state Nd-YAG laser, 1% of the active species Nd 3+ is doped into the crystal structure and produce stimulated emission at 1.064 μ m Diode lasers are based on emission of photon through electronic transition from the conduction to the valence band of semiconductors.
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Dr. P. Lucas U of A MSE 110 Redox reactions ELECTROCHEMISTRY 2 Fe + 3 / 2 O 2 Æ Fe 2 O 3 One element is giving off electrons while the other element is gaining these electrons. This can be divided in two half reactions : Elements normally gain or loose electrons according to the octet rule, hence the ions formed during redox reactions have the oxidation number predicted from the groups of the periodic table. (Na Æ Na + , Cl Æ Cl - ,S Æ S 2- ). One of the main classes of reactions in chemistry are called oxidation-reduction reactions or redox reactions . Oxidation-reduction reactions are characterized by the transfer of electrons between reactants. Fe Æ Fe 3+ + 3 e - oxidation Na Æ Na + + e - Na + 1 / 2 Cl 2 Æ NaCl = Fe 3+ 2 ,O 2- 3 = Na + ,Cl - O 2 + 4e - Æ 2 O 2- reduction Cl 2 + 2 e - Æ Cl - Therefore an oxidation-reduction (redox) reaction is the sum of an oxidation and a reduction. The two reactions necessarily always happen simultaneously.
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Dr. P. Lucas U of A MSE 110 Half reaction: oxidation reactions Oxidizing agents are species with high electronegativity. Oxygen being the second most electronegative element, it attracts electrons from other elements to form oxides. Hence the term oxidation originates from elements loosing electrons during reaction with oxygen. ELECTROCHEMISTRY Cu Æ Cu 2+ + 2 e - Cu metal being oxidized into blue Cu 2+ The oxidation reaction correspond to the loss of one or more electrons as illustrated in the following half reactions : Ca Æ Ca 2+ + 2 e - Na Æ Na + + e - Fe Æ Fe 3+ + 3 e - MnO 4 2- Æ MnO 4 - + e - These reactions are induced by an
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LECTURE 26 Electrochemistry - SUMMARY FROM LAST CLASS...

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