EMF as function of temperature

K has been measured carefully as function of temperature over a considerable temperature interval for each temperature K may be determined from conductivity or from emf measurements, the latter technique being described in Section 4.13(d). The heat of ionization per unit advancement of the ionization reaction may be determined according to Eq. (3.7.4) in conjunction with van t Hoff s Law. This requires a knowledge of the manner in which y changes with T. Details, based on Section 3.10, are to be handled in Exercise 4.4.1, which the reader is advised to work out in detail. 

Standard EMF, Slope Factor and Debye-Huckel Constant A (Unit Weight of Solvent) as Functions of Temperature... 

Figure 9.26, Comparison between experimentally determined and calculated EMF values as a function of temperature for various liquid alloys in Ga-Te (Oh and Lee 1992).

The emf of the lithium-aluminium system versus pure lithium in a Lil-KI-LiCl molten eutectic is shown in Fig. 8.2 as a function of temperature and composition. It can be seen that the emf remains constant (at about 300 mV more negative than pure lithium) in the range of stability of the /3-phase (-7-47 atoms per cent of lithium), thus implying a constant lithium activity in the alloy surface. At concentrations greater than 47 atoms per cent, the lithium activity becomes strongly composition-depen-dent. 

It can be seen in the above equation that the emf is a linear function of temperature. Thus, by measuring 8 and the temperature coefficient, we can obtain the thermodynamic properties of the cell, AG, AS, A//. 

After the cell has been in the thermostat bath for at least 10 min, measure the emf and repeat this measurement at least three times at 5-min intervals to verify that there is no systematic drift in the emf. The potentiometer circuit should be checked against the standard cell immediately before each reading. The emf should be determined as a function of temperature at four values in the range from 0 to 40°C, and an ice bath can be used for the 0°C measurement. 

Standard electrode potentials of the Ag-AgI electrode were determined in the temperature range 5 °-35°C in 20-80 wt % ethylene glycol + diethylene glycol mixtures by emf measurements on the cell Pt-H2(g, 1 atm)/HOAC (mt), NaOAC (m2) KX (m3)/AgX-Ag in the solvent. The standard molal potentials Em°, in the various solvent mixtures have been expressed as a function of temperature. The various thermodynamic parameters for the transfer of hydrogen iodide from ethylene glycol to these media at 25° C are reported, and their variation with solvent composition is discussed. The transfer free energies of the proton and the iodide at 25°C, on the basis of the ferrocene reference method with ethylene glycol as the reference solvent, are also reported in the mixtures. 

Some environmental limitations of the standard thermocouple materials compiled by ASTM [36] are reproduced in Table 16.11. The thermal EMF of standard thermoelements relative to platinum is shown in Fig. 16.20 [36]. Seebeck coefficients (first derivative of thermal EMF with respect to temperature) for each of the standard thermocouples as a function of temperature are tabulated in Table 16.12. 

Isothermal emf of cell (VI) in a sodium borate melt as a function of temperature (dynamic measurements) showing validity of Equation (26-33) and thermodynamically correct functioning of the cell with respect to the inherent oxygen/oxide system of the melt, (b) Effect of internal short circuit of platinum measuring electrode during a 10 h halt of the dynamic measurement after (a). 

The first set of tables below lists, for each thermocouple type, the emf as a function of temperature on the International Temperature Scale of 1990 (ITS-90). The coefficients in the equation used to generate the table are also given. The second set of tables gives the inverse relationships, i.e., the coefficients in the polynomial equation which expresses the temperature as a function of thermocouple emf. The accuracy of these equations is also stated. 

Thermocouple emf as a Function of Temperature in Degrees Celsius (ITS-90) emf in Millivolts Reference junctions at 0 °C... 

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