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 ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ________________________________________________________ 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 ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ________________________________________________________ Gibbs and the Cell Potential Here we can easily see how this Gibbs function relates to a potential. welectrical PotentialCh 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 ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ________________________________________________________ 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. dGo 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 ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ________________________________________________________ Enthalpy (H) Thermodynamic relationship H o Go TS o Since o Go nFE dEo H o nFE o T (nF ) dT dEo H o nF(E o T ) dT dEo S o nF Ehteram A Noor- Kng Abdulaziz University dT ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ 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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 .