Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
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Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction.......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) ............................... 31.2Thermodynamic Basis of the Standard. Formal, and EquilibriumPotentials.......................................................... 51.2.1The Problem of the Initial and FinalStates......................... 61.2.2Standard States and Activities......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) ............. 71.2.3Electrolytes. Mean Activity......................................... 71.2.4Electrochemical Potential. GalvaniPotential Difference.Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
............ 81.2.5Calculation of I from Calorimetric Data and AG*. AW*. AS* fromElectrochemical Measurements........................................ 1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction.......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) ical Measurements....................................... 111.2.8Determination of from Thermodynamic Data........................... 111.2.9The Formal Potential (E° )......................................... 121.2.10The Determination of E° by Cyclic Voltammetry...................... 13References..... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) .................................................... 15www.pdfgrip.ccHT)J1.1IntroductionPractically in every general chemistry textbook. one can findBard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
a table presenting the Standard (Reduction) Potentials in aqueous solution at 25 °C. sometimes in two parts, indicating the reaction condition: acidic1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction.......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) s). The former table is referred to in a chapter devoted to Electrochemistry (or Oxidation - Reduction Reactions), while a reference to the latter one can be found in a chapter dealing with Chemical Thermodynamics (or Chemical Equilibria). It is seldom indicated that the two types of tables contain Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) redundant information since the standard potential values of a cell reaction (E*u) can be calculated from the standard molar free (Gibbs) energy changBard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
e (AG*) for the same reaction with a simple relationship““ nF \nF /where n is the charge number of the cell reaction, which is the stoichiometric numb1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction.......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) ction. R is the gas constant, and T is the thermodynamic temperature. However. E*n is not the standard potential of the electrode reaction (or sometimes called half-cell reaction). which is tabulated in the tables mentioned. It is the standard potential of the reaction in a chemical cell which is eq Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) ual to the standard potential of an electrode reaction (abbreviated as standard electrode potential). E* when the reaction involves the oxidation of mBard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
olecular hydrogen to solvated protonsjH2(g)-----»H+(aq) + e- (2)The notation H + (aq) represents the hydrated proton in aqueous solution without speci1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction.......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) eason why we speak of reduction potentials. In the opposite case, the numerical value of £* would be the same but the sign would differ. It should be mentioned that in old books, for example, in Latimer’s book[l], the other sign convention was used; however, the International Union of Pure and Appli Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) ed Chemistry (IUPAC) has introduced the unambiguous and authoritative usage in 1974 [2. 3].www.pdfgrip.com4 I 1 Standard Potential!Although the standaBard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
rd potentials, at least in aqueous solutions, are always related to reaction (2). that is. the standard hydrogen electrode (SHE) (sec Ch. 18.3). it do1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction.......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) ential, £«11. when both electrodes arc at equilibrium. The cell as a whole is not at equilibrium (for if the cell reaction reaches its equilibrium then £«|| = AG'«n = 0): however, no current flows through the external circuit, with all local charge-transfer equilibria across phase boundaries (except Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) at electrolyte-electrolyte junctions) and local chemical equilibria within phases being established.One may think that AG* and £* values in the tableBard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
s cited are determined by calorimetry and electrochemical measurements. respectively. It is not so: the way of tabulations mentioned serves practical 1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction.......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) e easier or were more reliable. On the other hand. £* values displayed in the tables mentioned have been determined mostly by calorimetric measurements since in many cases - owing to kinetic reasons, too slow or too violent reactions - it has been impossible to collect these data by using the measur Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) ement of the electric potential difference of a cell at suitable conditions. Quotation marks have been used in writing “thermodynamic”, as £* is per sBard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006)
e also a thermodynamic quantity.In some nonaqueous solvents, it is necessary to use a standard reaction other than the oxidation of molecular hydrogen1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction.......................... Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) . saturated calomel, SCE. or silver/silver chloride) can also be used in organic solvents, much effort has been taken to find reliable reference reactions. The system has to meet the following criteria: Bard a j , stratmann m , scholz f encyclopedia of electrochemistry, inorganic chemistry volume 7 (2006) 1Standard PotentialsGyorgy ImeltDepartment of Physical Chemistry, Edtvổi Lorand University, Budapest, Hungary1.1Introduction..........................Gọi ngay
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