Electro-motive force

Electro-motive Force.—Helmholtz showed, as early as 1889, that the dissociation of water could be theoretically calculated from the electro-motive force of polarization, but in this particular case the counter E.M.F. of the reversible decomposition of water cannot be directly determined. In other cases, however, the method has proved itself applicable e.g. from the E.M.F. of the hydrogen-chlorine gas cell and the HCl-vapour tension of the acid used, the dissociation of hydrochloric acid can be determined at ordinary temperatures, and then that at very high temperatures obtained with the aid of the molecular heats of the reacting gases, which have been measured by Pier up to very high temperatures (25). 

Calculation of a New Equilibrium from Other Equilibrium Measurements.—This method is capable of very numerous applications. My co-workers and I determined the equilibrium of the two reactions— 

In connection with the dissociation of water vapour, reference may be made also to the following application The dissociation of hydrochloric acid, 

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Science of study of a process where a chemical change generates electricity or vice versa as in the charging of an electro-chemical cell, when the imposed electro-motive force pushes the electrically-charged ions to a higher energy state, is referred to as Electro-chemical Thermodynamics. ... 

Electro- motive force Tempera- ture, degrees Centigrade Electro- motive force Tempera- ture, degrees Centigrade... 

The potential free energy associated with the formation of the proton gradient is called the proton motive force (PMF), the counterpart of the electro-motive force (EMF), and represented by the symbol ApH - PMF consists of two components, one of which is associated with the difference between the proton concentrations on the inside (i) and outside (o) of the membrane, i.e., ([H ]j - [H ]q). As proton concentration can be expressed in terms of pH, the proton-concentration difference can be written as ApH, i. e., -log,([H ] / [H o), and the potential difference in volts written as 2.3(RT/c ApH where< is the Faraday constant. The second component of PMF arises from the fact that protons are positively charged, and so there is an electro-static transmembrane potential, designated as AT. When PMF, Apn% is expressed as the sum of the proton-gradient term and the membrane-potential term, we have... 

The Effect of Temperature on Gibbs Free Energy and Electro motive Force. When the entropy S is eliminated from equations (18) and (22) we obtain... 

E = electro-motive force, F = 96540 coulombs). This is one of the most convenient and accurate methods for the determination of A, but it is limited, unfortunately, to special cases. 

We have already pointed out that the electro-motive force of a galvanic cell is proportional to the affinity of the... 

In this way the general solution has been obtained to the problem which I originally propounded, namely, the calculation of the maximum work (free energy, chemical affinity, electro-motive force, vapour pressure, etc.) from purely thermal quantities, namely, specific heats, heats of transformation, heats of reaction of all sorts or, expressed in more general terms, whereas before U could be calculated when A was known for all temperatures but not the converse, the latter is now also possible. 

The electro-motive force of the hydrogen-chlorine gas cell is well known from this the dissociation of hydrochloric acid gas may be derived, knowing the HCl-vapour pressure of the solutions used. With the further assistance of the equilibrium in the Deacon process,... 

Of particular importance is the result of a similar calculation, namely, the derivation of the electro-motive force of the oxy-hydrogen cell from the dissociation of water vapour. Calculation, the principle of which dates back to Helmholtz, led v. Wartenberg and me (1906) to the result... 

The variation of the temperature of the copper block K, relative to that of the block C, caused by the introduction of the substance, is determined by means of ten copper-constantan couples in series, the electro-motive force being measured by means of a Siemens and Halske millivoltmeter. As these instruments allow very accurate readings to be taken, using a lens if necessary, it was possible to employ one of them instead of a mirror galvanometer. 

We have already (p. 115) had an example of such an application the values found by U. Fischer for the heat of formation of silver iodide by means of formulae (99) and (100) should be more reliable than that obtained by equation (1). For though the electro-motive force of the cell in question could be determined at one temperature with sufficient accuracy (about 1 per 1000), the temperature coefficient could not be obtained so precisely as to allow the determination of U also to 1 per 1000 by equation (1) for the use of formula (100), on the other hand, the specific heats need be known with only moderate accuracy, since they serve only to determine the relatively small difference A — U. The case is similar in the following example. 

TANAi"AM] Tanaka, H., Yamaguchi, A., Moriyama, J., Standard free energies for the formation of fluorides in several metals by electro-motive force measurements, Nippon Kinzoku Gakkaishi, 35, (1971), 1161-1164, in Japanese. Cited on pages 201, 5 3 3. 

It is easy to measure this free energy in reactions that transfer electrons, since these electrons can be harnessed to give an electric current. The power of an electric current to do work depends upon the voltage (or electro-motive force) imder which it is produced, and electromotive force can be very exactly measured. Suppose we want to know the free energy of the reaction... 

And now briefly about modem Ukrainian fuel cell history Being based on many years positive experience in manufacture of real nano-sized zirconia powders with different stabilizers like yttria, calcia, scandia etc. and zirconia ceramics [8, 9] the first Ukrainian demonstrating model of zirconia fuel cell was made and exhibited by January 22, 2002 [10- 12]. It has realized 0.85 V and 0.5 V of electro motive forces with propane gas and ethanol respectively at their direct burning. 

Tanaka, H., Kishida, Y, Moriyama, J., Standard Free Energies for the Formation of UFeC2 and UWC2 by Electro-Motive Force Measmements (in Japanese), J. Jpn. Inst. Met., 37, 564-567 (1973) (Crys. Structure, Experimental, Phase Diagram, Phase Relations, Thermodyn., 11)... 

For the electrode pair Zn Cu considered, a characteristic potential difference (electro motive force, emf) of 1.10 volt is found at standard conditions. 

Bezboruah, C.P., Camoes, M.F.G.F.C., Covington, A.K., and Dobson, J.V. (1973) Enthalpy of ionization of water from electro-motive force measurements. 

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