Temperature dependence of emf

Smedley, The Interpretation of Ionic Conductivity in Liquids, reprint ed.. Books on Demand, Ann Arbor, MI (1980). 

Conductance and Transference Determinations, in B. W. Rossiter and J. F. Hamilton (eds.), Physical Methods of Chemistry, 2d ed., Vol. II, chap. 8, WUey-Intersdence, New York 

In this experiment the following electrochemical cell is stndied  

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Having determined the temperature dependence of emf as the gradient of a graph of emf against temperature, we obtain the value of AS(Ceii) as gradient x n x F . 

FIGURE 4.9 Temperature dependence of emf for zirconia single-crystal sensors with a molten metal-metal oxide RE. Measuring gas is air. ( ) In-i-lnjOj RE and (o) Bi-BijOj RE. Symbols with full line represent data taken during heating and cooling. (From Zhuiykov, S., Zirconia single crystal analyser for low-temperature measurements, Proc. Control and Quality 11 (1998) 23-37. With permission.)... 

Taking another example to illustrate the dependency of emf on concentration (temperature effect is not considered, as in the previous example), reference may be drawn to the familiar Cu-Zn cell a shown in standard notation as ... 

The temperature dependence of the emf of an electrochemical cell can often be written in the form... 

Standard emf Values for the Cell H2/HCl/AgCl, Ag in Various Aqueous Solutions of Organic Solvents at Various Temperatures Temperature Dependence of the Standard Potential of the Silver Chloride Electrode Standard Electrode Potentials of Electrodes of the First Kind Standard Electrode Potentials of Electrodes of the Second Kind Polarographic Half-Wave Potentials (E1/2) of Inorganic Cations Polarographic E1/2 Ranges (in V vs. SCE) for the Reduction of Benzene Derivatives Vapor Pressure of Mercury... 

AjG data for B-TiO are reviewed on the table for a-TiO (9). Values of A H derived from a G" depend on the value of S (see Entropy). There are additional references on the A G which deserve comment. Solid-state emf data of Hoch et al. ( ) are insufficient to yield AjG (B), especially in the direct way used by Drowart et al. (19). Their interpretation is inconsistent with phase diagrams (, 1 ) and extensive emf data (7) which show bivariant behavior in which A C(02) is a strong function of (0/Tl). It is not useful to reinterpret the emf data ( 8) they show a temperature dependence of the wrong sign and we do not know the necessary electrode compositions. The often quoted A G of Kubaschewski and Dench (2 1) is not an independent value since it assumes the correctness of the calorimetric data of the Bureau of Mines (, 1 ). Kubaschewski s reassessment (, 8) of... 

Modem digital voltmeters allow the measurement of highly accurate emfs. If the emfs are measured over a range of ionic strengths this will allow the effect of ionic strength on the equilibrium constants to be studied in detail. Furthermore if the dependence of emf on temperature is measured, the thermodynamic quantities. A//, A5 and AC can be found and interpretations of the magnitudes made. If the experimental set-up can be adapted to a determination of the emfs at various pressures to be made, then AV values can also be found. 

Figure 26-20. Practical signincance of thermoelectric potentials. The relative potentials, tRpt< of a platinum electrode in melts satisfying Equation (26-33) were obtained from standiud thermoelectric potentials, of a zirconia electrode and temperature-dependent emfs, E, of cell (VI) according to Equation (26-37). The temperature dependence of Pp, is determined by the standard Seebeck coefficients of the melts and is positive (a), negative (b), and, depending on the temperature, both negative and positive (c).

Hamed and Hamer [14] determined experientially the temperature dependence of the EMF of the lead—acid cell within the range from 0 to 60 °C for acid concentrations varying between 0.05 and 7.0 M H2SO4, and represented it by the following empirical equation ... 

A study of the temperature dependence of the emf made it possible to determine the dependence of AG on T and thus find the change in the entropy AS and enthalpy AH resulting from the formation of GaP ... 

Figure 1 shows the temperature d endences of the emfs obtained for four cells. The constant value of the emf was established after 5—10 h from the banning of a run. Subsequently, stable values (within 0.2 mV) were reached immediately after the establishment of a constant temperature. The emfs of all the cells did not vary appreciably with time and were easily reproduced durli cyclic variation of the temperature. The values obtained were similar for alloys of different composition within the same heterogeneous region, which indicated reversible operation of the galvanic cells. The temperature dependences of the emfs of cells... 

The temperature dependence of the emf enabled us to estimate entropy and the heat of formation of the higher bismuth and antimony tellurides and selenides. These two quantities were deduced from... 

The experimental results, analyzed by the least-squares method, jrielded the temperature dependences of the emf s listed in the third column of Table 1. 

The results presented in Table 1 were analyzed by the least-squares method to give the coefficients a and b in the linear temperature dependence of the emf of the cell (1) E -= a + 6T. In this way, we obtain the equation... 

The temperature curves of the thermal emf of binary and ternary alloys of copper with iron and cobalt were measured in the range of 2 to 300 K [1974Bei]. It was shown that the iron and cobalt contributions to the thermal emf are practically independent, which means that for the ternary alloys, it is essentially the superposition of the contributions from the binary alloys. This gives the possibility of determining the compositions of alloys for low temperature thermocouples with a given temperature dependence of the thermal emf. 

According to Eqs. (45)-(47) the emf of a galvanic cell contains different thermodynamic information. The emf makes it possible to determine the Gibbs energy of the cell reaction and the chemical potentials of the electrode components or the partial pressures of gases. It shall be mentioned here that reaction enthalpies and reaction entropies can also be deduced from the temperature dependence of the emf. More details on thermodynamic investigations will be given in Section V.A. 

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