   # Engineering Materials Week 12

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Engineering Materials Week 12
17.7 An electrochemical cell is constructed such that on one side a pure Zn electrode is I contact with a solution containing ions at a concentration of M. The other cell half consists of a pure Pb electrode immersed in a solution of ions that has a concentration of M. At what temperature will the potential between the two electrodes be +0.568 V?

17.15 (a) Cite the major differences between activation and concentration polarizations.
Activation polarization is the condition wherein a reaction rate is controlled by one step in a series of steps that takes place at the slowest rate. Concentration polarization occurs when a reaction rate is limited by diffusion in a solution.
(b) Under what conditions is activation polarization rate controlling?
When the reaction rate is low and/or the concentration of active species in the liquid solution is high.
(c) Under what conditions is concentration polarization rate controlling?
When the reaction rate is high and/or the concentration of active species in the liquid solution is low.
17.26 (a) What are inhibitors?
Substances that when added to a corrosive environment in relatively low concentrations, decrease the environment's corrosiveness.
(b) What possible mechanisms account for their effectiveness?
Attachment of inhibitor molecules to the corroding surface so as to interfere with either the oxidation or reduction reaction; and the formation of a very thin and protective coating on the corroding surface.
17.31 (a) Determine whether the oxidation kinetics obey a linear, parabolic, or logarithmic rate expression.

From the first two equations K₁= 0.238 and K₂ = 14.2; while from the second and third equations K₁ = 0.117 and K₂ = 44.5. Thus, a parabolic rate expression is not obeyed by this reaction.
6.16 = 100K₃
8.59 = 250K₃
1 2.72 = 1000K₃
And the three K₃ values may be computed which are 6.16 x , 3.44 x , and 1.272 x . Since these K₃ values are all different, a linear rate law is not a

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