Thermo_ISM_ch11

# Thermo_ISM_ch11 - Questions on Concepts Q11.1) What is the...

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196 Questions on Concepts Q11.1) What is the difference in the chemical potential and the electrochemical potential for an ion and for a neutral species in solution? Under what conditions is the electrochemical potential equal to the chemical potential for an ion? z µ µφ =+ % . For a neutral species, the chemical potential and electrochemical potential have the same value. They differ by z φ for an ion. The electrochemical potential is equal to the chemical potential for an ion if = 0. Q11.2) Show that it follows from ( ) H , 0 for all f Ga q T + ∆= o that the potential of the standard hydrogen electrode is zero. () 2 2 / 1 2 and H , 0 H H H f HH H q FF µµ φµ + + + + + == = = oo o o Q11.3) To determine standard cell potentials, measurements are carried out in very dilute solutions rather than at unit activity. Why is this the case? In order to determine the standard potential, the mean ionic activity must be known. It can be calculated in dilute solutions using the Debye-Huckel limiting law, but there is no reliable way to calculate the activity coefficient near unit activity. Q11.4) Explain why it is possible that the magnitude of the maximum work available from a battery can be greater than the magnitude of the reaction enthalpy of the overall cell reaction. 1 i f 0 electrical TS wG H H S H ⎛⎞ = −∆ > −∆ ∆ < ⎜⎟ ⎝⎠ Q11.5) The temperature dependence of the potential of a cell is vanishingly small. What does this tell you about the thermodynamics of the cell reaction? Because ,0 R RR P P G E Sn F S TT ∂∆ = ∆≈ ∂∂ o o Q11.6) Why is the capacitance of an electrolytic capacitor so high compared with conventional capacitors?

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197 The positive and negative plates of an electrolytic capacitor are separated by an extremely small distance (the thickness of the electrical double layer, essentially). And so, the electric field is very strong and the capacitance large. , 30A A d d ε ⎛⎞ ⎜⎟ ⎝⎠ o ± Q11.7) Can specifically adsorbed ions in the electrochemical double layer influence electrode reactions? Yes, specifically adsorbed ions can play a central role in the atomic-scale processes occurring on an electrode surface (e.g. Cl - on Cu electrode). Q11.8) How can one conclude from Figure 11.18 that Cu atoms can diffuse rapidly over a well-ordered Au electrode in an electrochemical cell? The copper atoms would be dispersed randomly over the Au surface if they could not diffuse laterally. Instead, they are seen only in islands and on edges, where they are tightly bound. They must have diffused there freely over the surface. Q11.9) How is it possible to deposit Cu on a Au electrode at a potential lower than that corresponding to the reaction Cu 2+ ( aq ) + 2e ± Cu( s )? Cu 2+ is more tightly bound to the Au surface than to Cu. Thus a lower potential is needed to reduce Cu 2+ onto the Au surface.
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## This note was uploaded on 06/10/2010 for the course CHEM 127 taught by Professor Nefzi during the Spring '03 term at UCSD.

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Thermo_ISM_ch11 - Questions on Concepts Q11.1) What is the...

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