CHAPTER VII Electrochemical Thermodynamics

Prepared by Dr. Ehteram A. Noor Associate Prof. of physical chemistry

Revised by Dr. Salwa Al-Rashid Associate Prof. of physical chemistry

Ehteram A Noor- Kng Abdulaziz University

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Gibbs Function and Electrical Work Start with the First Law of Thermodynamics and some standard thermodynamic relations. We find

dE  dq  dw dq = T dS

dw  PdV  dwelectrical

dE  TdS  PdV  dwelectrical dHP  dEP  PdV

dGT  dHT TdS

dGT  dET ,P  PdV TdS

dGT  TdS  PdV  dwelectrical  PdV TdS

dGT,P  dwelectrical And therefore, the Gibbs function is at the heart of electrochemistry, for it identifies the amount of work we can extract electrically from a system. Ehteram A Noor- Kng Abdulaziz University

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Gibbs and the Cell Potential Here we can easily see how this Gibbs function relates to a potential.

welectrical  PotentialCh arg e  EQ

GT ,P  welectrical and Q  nF

GT ,P  nFE By convention, we identify work which is negative with work which is being done by the system on the surroundings. And negative free energy change is identified as defining a spontaneous process. Note how a measurement of a cell potential directly calculates the Gibbs free energy change for the process. Ehteram A Noor- Kng Abdulaziz University

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Variation of e.m.f with temperature One of the most rewarding aspects of electrochemistry is that ΔS values spring directly from studies of the temperature variation of e.m.f. dGo dEo Since o o  nF G  nFE dT dT

o where ( dE / dT ) is the temperature coefficient of the electrochemical cell Look at this equation important relationship between numerical factors and Eo can be obtained

Entropy (S) o  G  o Thermodynamic relationship    S  T P

dEo dEo S o S o  nF  dT dT nF Ehteram A Noor- Kng Abdulaziz University

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Enthalpy (H)

Thermodynamic relationship H o  Go TS o

o o dE Since o o S  nF G  nFE dT

dEo H o  nFE o T (nF ) dT

dEo H o  nF(E o T ) dT

Ehteram A Noor- Kng Abdulaziz University

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Ehteram A Noor- Kng Abdulaziz University

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Ehteram A Noor- Kng Abdulaziz University

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Ehteram A Noor- Kng Abdulaziz University

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Text resources J. M. Seddon and J. D. Gale, Thermodynamics and Statistical Mechanics, The Royal Society of Chemistry, (2001) G. W. Castellan, Physical Chemistry, 2nd Edn. (1971), Adison-Wesley Publishing Company, Amesterdam I. Tinoco, Jr, K. Sauer and J. C. Wang, Physical Chemistry, (1978), Prentice-Hall, Inc., New Jersey W. J. Moore, Basic Physical Chemistry, (1983), Prentice-Hall, Inc., New Jersey J. R. Wan and A. P. H. Peters, Concise Chemical Thermodynamics, 2nd Edn. (1996), Taylor & Francis e-Library.http://www.ebookstore.tandf.co.uk/.” R. J. Silbey and R. A. Alberty, Physic al Chemistry, 3rd Edn. (2001), John wiley & Sons, New York. I. N. Levine, Physical Chemistry, 5th Edn. (2003), McGraw-Hill, New York.

Electronic Web resources mmadou.eng.uci.edu/classes/MAE-212/MAE212.II.pptx

Ehteram A. Noor- King AbdulAziz University