LECTURE 29 Corrosion - SUMMARY FROM LAST CLASS...

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Dr. P. Lucas U of A MSE 110 Electrochemistry Equilibrium is reached when the concentration of reactants and product doesn’t change with time any more. If the concentration of a reactants or product is increased the equilibrium is shifted in a way that consumes that species. The equilibrium state is defined by the equilibrium constant K which specify the concentration of the species in solution at equilibrium. Cu 2+ + Zn ' Zn 2+ + Cu The equilibrium constant defines how complete the reaction is at equilibrium. The driving force of a reaction depends on the concentration of reactants. If the concentration of ions of the reductant couple is [Red] (i.e: [Zn 2+ ]) and the concentration of ions of the oxidant couple is [Ox] (i.e: [Cu 2+ ]): The potential of each electrode then also depend on the concentration of reactants. SUMMARY FROM LAST CLASS equ equ Cu Zn K ] [ ] [ 2 2 + + = Equilibrium constant ] x [ ] [Red ln RT G G o O + Δ = Δ ] [ ] Red [ ln RT E E o Ox nF Δ = Δ ]) [ ln RT E ( - ]) [ ln RT (E E 2 o Zn/Zn 2 o Cu/Cu 2 2 + + + + = Δ + + Zn nF Cu nF
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Dr. P. Lucas U of A MSE 110 Corrosion of metals Spontaneous redox reactions such as the one that take place in batteries are very useful. CORROSION However some redox reactions can be very destructive. × 10 Billions $ spent in the US each year to repair damage from corrosion. 20% of steel produced in the US every year is used to replace corroded parts. Corrosion is the deterioration of metals by spontaneous redox reactions.
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U of A MSE 110 Corrosion of metals Example: Zn in acid solution: E o (Zn/Zn2+) = -0.76 Zn ' Zn 2+ + 2e - CORROSION Zn + 2H + Æ Zn 2+ + H 2 At some region on the metal the Zn will be oxidized Zn ' Zn 2+ + 2e - Since Zn is a metalic conductor, the e - are transferred to an adjacent region where H + is reduced: 2H + + 2e - ' H 2 . E
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LECTURE 29 Corrosion - SUMMARY FROM LAST CLASS...

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