Electromotive Force emf Method

Out of Equations 17.62 and 17.63 the transference number is calculated in the useful differential form to neglect the concentration dependence of the transference number [436]  

The advantage of this method is the application over wide concentration ranges and the currentless, that is, nondestructive measurement. In contrast, the availability of the activity coefficient or of an adequate nonaqueous salt bridge and reversible electrodes is required. Some authors evade these problems by assuming a constant activity coefficient over the whole concentration range [88, 449]. 

AU these classical methods of determining transference numbers, Hke Hittorf, moving boundary, and emf, have been developed and used for aqueous systems. They involve high experimental costs when applying them for electrolytes with organic solvents and especially for hthium salts. To measure transference numbers of the hthium cation in electrolytes for hthium-ion batteries, the search for a rapid method that gives precise values is still going on. 

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Electrochemical HPLC detectors, 15 Electromotive force (EMF) method, pXa values and, 9,12 Ephedrine, 5... 

The thermodynamic properties of aluminum antimonide have been previously studied by the electromotive force (emf) method using aluminum chloride as the electroljrte in fused lithium and potassium chlorides [4], The calculated value [4] of the standard entropy of solid aluminum antimonide S 98 = 6.0 0.8 eu/g-atom and that obtained by Piesbergen [5] from measurements of low-temperature specific heat, = 7.68 0.05 eu/g-atom do not agree even within the... 

The electromotive force (EMF) generated by electrochemical cells can be used to measure partial Gibbs energies which, like vapour pressure measurements, distinguishes these methods from other techniques that measure integral thermodynamic quantities. Following Moser (1979), a typical cell used to obtain results on Zn-ln-Pb is represented in the following way ... 

Figure 5. The apparatus for the electromotive force(EMF) measurements(An S02 gas concentration cell method).

Here, V and Eq are cell potentials or terminal voltage at arbitral current density I and 1 = 0. Usually, E(-) is called a tliermodynamic electromotive force, EMF. The notations of A and 5 are a surface area and thickness of the ceramic electrolyte, and s is an electric conductivity. Since measurement was carried out by a direct current method, the s value corresponded to an overall one including the contributions of anode and cathode polarities as well as the protonic conductivity of ceramic electrolyte. The dependence of Eq on temperature was very small and almost independent of it. On the other hand, the Eq values slightly depended on the input CH4/H2O ratio. 

Determination of the activity coefficients of the non-volatile solute in a solution is difficult. If electrolytes (ions) are present, the activities can be obtained from experimental electromotive force (EMF) measurements. However, for non-electrolyte and non-volatile solutes an indirect method is applied to find initially the activity of the solvent over a range of solute concentrations, and then the Gibbs-Duhem equation is integrated to find the solute activity. If the solution is saturated, then it is easy to calculate the activity coefficient... 

A particularly elegant method to determine the equilibrium constants is, when possible, to use the measurement of electromotive forces (emf) of galvanic elements or electrochemical cells. 

Experimental studies are the primary iriformation sources for thermodynamic properties and phase diagrams of all systems. The method of electromotive force (EMF) is one of the most important methods of the physicochemical analysis. One peculiarity of the EMF is its proportionality to the chemical potential ... 

The accuracy of the proposed experimental technique does not yield the best calorimetric measurements and completeness of the information obtained by the EMF exceeds the calorimetric methods in some case. So, the proposed variant of the EMF can be called as universal and self-sufficient, and the cost of equipment used in the EMF method is much lower than the calorimetric one. EMF remains one of the most important methods in metallurgical thermodynamics.The method of electromotive force (EMF) with proposed electrocemical cells is a powerful tool to study the thermodynamic properties of metaUic, semiconductor and oxyde systems. It permits to identify a set of values of the chemical potentials of one of the component of the different phases. The final result of this work consist of the thermodynamic optimization of the studied system. 

CA 55, 17007 (1961) [A new method has been described, based on measuring the electromotive force in a conductor moving in a magnetic field with expln products. A Cu or Al foil 0.3-0.5 mm thick was used as the conductor, the emf being recorded by means of a cathode-ray oscillograph, and the speed (u) being ealed from the equation u = (r/Hl) x 10 cm/sec... 

Because the electromotive force of this cell falls rapidly after the polarizing current ceases to flow, it is sometimes measured at exact intervals after the circuit is broken. By graphical extrapolation of the obtained values the initial back electromotive force at zero time is found i. e. at the instant of switching off the current. This method is only satisfactory with lower current densities. For higher currents the fall of EMF is so rapid that the extrapolation to the moment of a break in the circuit is no longer reliable. For more accurate measurements registration potentiometers are used which automatically register... 

In a short chapter in a book of this nature it is quite futile to attempt any comprehensive discussion of electromotive force. Only the fundamental notions can be indicated The student is therefore referred to the textbooks dealing specifically with Electrochemistry, especially Le Blanc s Electrochemistry (English or German edition), Lehfeldt s Electrochemistry (in this series of textbooks), and the recent work by Allmand, Applied Electrochemistry This latter book is of special significance in showing the scientific application of pure electrochemistry to industrial problems As regards laboratory experimental methods, i e the measurement of emf, details may be found in any of the textbooks on practical physical chemistry VOT.. II. 113 10... 

Froment et al. [164,166] measured the carbon activities in the homogeneity range of boron carbide by electromotive force method (emf, potentiometric... 

A new method for using photo-electromotive force (Photo-EMF) in the detection of gas and for controlling sensitivity is proposed (Vashpanov et al., 2011). Photo-EMF on the heterojunction between the PSi thin layer and the crystalline silicon wafer depends on the concentration of ammonia in the measurement chamber. A light-transparent contact to the porous Si was formed. Photo-EMF sensitivity corresponding to the ammonia concentration in the range from 10 ppm to 1000 ppm can be controlled by the intensity of the source of illumination. 

Direct potentiometric method The sample and standard solutions are introduced into the potentiometric measuring cell mixed with background electrolyte. The fluoride ion-selective electrode and appropriate reference electrode (saturated calomel electrode or silver/silver chloride electrode with double jimction is recommended) are dipped into the solution and the electromotive force is measured. An EMF versus log (fluoride ion concentration) calibration curve is used for evaluation. 

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