L23 - SUMMARY FROM LAST CLASS Phase Diagrams Binary phase...

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Dr. P. Lucas U of A MSE 110 Phase Diagrams SUMMARY FROM LAST CLASS Binary phase diagrams: two components A and B The binary phase diagram describes the phase stability domains of a system of two compounds or elements A and B as a function of temperature T and composition (mole %) . Since we only have two axes the third variable P is fixed (P=1 atm). There are three possible behaviors for a mixture of two components A and B. Complete solid solution: A and B same structure and size, B atoms substitute A continuously from pure B to pure A. A and B immiscible: limited solid solubility of A in B leads to phase separation and produce a large domain with two solid phase. At the eutectic composition the two phases melt simultaneously. Eutectic reaction: α + β ' L. A and B form a compound of different structure and composition: a compound melts congruently if it transforms into a liquid phase of the same composition. For domains where a solid and liquid phase are in equilibrium, the lever rule gives the amount of each phase: ; liq sol sys sol L X X X X L S L W = + = liq sol liq sys S X X X X L S S W = + =
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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 the main class of reaction in chemistry are called oxidation-reduction reaction or redox reactions . Na + 1 / 2 Cl 2 Æ NaCl = Fe 3+ 2 ,O 2- 3 = Na + ,Cl - Fe Æ Fe 3+ + 3 e - oxidation Na Æ Na + + e - O 2 + 4e - Æ 2 O 2- reduction Cl 2 + 2 e - Æ Cl - Oxidation-reduction reactions are characterized by the transfer of electrons between reactants. One element is giving off electrons while the other element is gaining these electrons. This can be divided in two half reactions : Therefore an oxidation-reduction (redox) reaction is the sum of an oxidation and a reduction. The two reactions necessarily always happen simultaneously. 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- ).
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Dr. P. Lucas U of A MSE 110 Half reaction: oxidation reactions 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 - The loss of electrons generates a positive charge and corresponds to an increase of the oxidation number of the oxidized species.
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