Electromotive force calculation

As a result, the electromotive force (EMF) of the cell is zero In the presence of fluoride ions, cerium(IV) forms a complex with fluoride ions that lowers the cerium(IV)-cerium(IIl) redox potential The inner half-cell is smaller, and so only 5 mL of cerium(IV)-cenum (III) solution is added To the external half-cell, 50 mL of the solution is added, but the EMF of the cell is still zero When 10 mL of the unknown fluonde solution is added to the inner half-cell, 100 mL of distilled water IS added to the external half-cell The solution in the external half-cell is mixed thoroughly by turning on the stirrer, and 0 5 M sodium fluonde solution is added from the microburet until the null point is reached The quantity of known fluonde m the titrant will be 10 times the quantity of the unknown fluoride sample, and so the microburet readings must be corrected prior to actual calculations... 

If At is known (say from measurements of electromotive force) we can calculate K, and rice versa. 

Electrochemical Method.—In this the value of the equilibrium constant K is calculated from the maximum work measured by means of the electromotive force of a voltaic cell (cf. Chap. XVI.). 

Thus, if we find how the electromotive force changes when the temperature of the cell is altered on open circuit, i.e., when no current is passing, we can at once calculate A, the latent heat, just as we can calculate the latent heat of evaporation of a liquid when we know the variation of its vapour pressure with temperature. Since E changes only slightly with T, we can evaluate dE... 

The heat of formation of a substance iji a voltaic cell may therefore be calculated from the measured Peltier effects and the electromotive force. 

The theory of concentration cells was first developed with great generality by Helmholtz (1878), who showed how the electromotive force could be calculated from the vapour pressures of the solutions, and his calculations were confirmed by the experiments of Moser (1878). 

The electromotive force of a cell with solutions of given concentrations may be calculated by subtracting the electrode potentials so obtained. 

Calculation of Chemical Equilibria from Measurements of Electromotive Forces and Vice Versa. 

If E is the electromotive force of the cell, and if r faradays are transported through the cell during the change for which the maximum work is calculated, we have ... 

Equation (6) therefore gives us a means of calculating chemical equilibria from measurements of electromotive force, and vice versa. It must be remembered that E has a sense only when it refers to a reversible cell if the cell is not reversible this simply means that no equilibrium can be set up at its electrodes between the reacting materials. 

Finally, we may observe that measurements of electromotive force can often serve to distinguish which kind of ions are really present in a solution. A concentration cell containing a solution of a known ion with an electrode reversible to the latter on one side, and the given solution with a similar electrode on the other side is taken. From its electromotive force, the concentration of the particular ion is calculable. In this way, for example, it was found... 

Application of Nernst s Theorem to the Calculation of Electromotive Forces Condensed Reactions. 

The rule for the calculation of the electromotive force of such a cell is, therefore, according to Nernst (cf. Bed. Ber., 1909,. p. 247) extrapolate the thermochemical data to the lowest possible temperature and put ... 

Shedlovsky et al. studied mixtures of sodium decyl, dodecyl, and tetradecyl sulfates by electromotive force measurements and determined the extent of the dissociation of the sodium counterions by the micelles. From the data obtained strong interaction below the CMC was found for all of the mixtures except those containing more than 25 mol % of sodium decyl sulfate [122]. Commercial alcohol sulfates are mixtures of homologs with different hydrocarbon chains. It has been demonstrated [123] that the CMC of such products is lower than that expected by calculation from the linear relationship between log CMC and the number of carbon atoms of the alcohol as stated in Eq. (11). These results are shown in Fig. 9. 

In writing the Etudes de dynamique chimique (1884), van t Hoff drew on Helmholtz s 1882 paper but especially on the work of August Horstmann, a student of Bunsen, Clausius, and H. Landolt.59 As has often been discussed, van t Hoffs was an ambitious and original synthesis of disconnected ideas and theories about opposing forces, equilibrium, active masses, work and affinity, electromotive force, and osmotic pressure. He demonstrated that the heat of reaction is not a direct measure of affinity but that the so-called work of affinity may be calculated from vapor pressures (the affinity of a salt for its water of crystallization), osmotic pressure (affinity of a solute for a solution), or electrical work in a reversible galvanic cell (which he showed to be proportional to the electromotive force). 

Thus, in the decades after 1880, many physicists and some chemists especially interested in mathematical approaches to their subject matter turned their attention to the calculation of free energies in both physical and chemical processes, with renewed attention to heat capacities, electromotive force, and values for molecular weights and molecular concentrations. Studies of reaction rates became more and more common, following up on path-breaking work by the physicist L. Wilhelmy and the chemist Vernon Harcourt.65... 

Calculation of Electromotive Force for an Overall Redox Reaction. In this case, there are two half-reactions ... 

The standard electromotive force (emf), °q, at equilibrium (no current flowing) under standard conditions is then calculated as follows ... 

The electromotive force (EMF) of this cell calculated from the potentials of the halfcells is equal to 1.593 V. Basic information about this cell are given by Vincent and Scrosati [319]. 

Fig. 8 The dependence of the electromotive force (EMF) ofCd(ll) ion-selective electrode on logarithm of Cd(ll) concentration in M NaNOs at pH 7. Solid lines, calculated response curves on the basis of Eq. (7) in Ref 399.

Dependence of Electromotive Force on Concentrations Calculate the electromotive force (in volts) registered by an electrode immersed in a solution containing the following mixtures of NAD+ and NADH at pH 7.0 and 25 °C, with reference to a half-cell of E ° 0.00 V... 

Activity coefficients of ions are determined using electromotive force, freezing point, and solubility measurements or are calculated using the theoretical equation of Debye and Htickel. 

However, electrochemical cells are most conveniently considered as two individual half reactions, whereby each is written as a reduction in the form indicated by Equations2.ll and 2.12. When this is done and values of the appropriate quantities are inserted, a potential can be calculated for each half cell of the electrode system. Then the reaction corresponding to the half cell with the more positive potential will be the positive terminal in a galvanic cell, and the electromotive force of that cell will be represented by the algebraic difference between the potential of the more-positive half cell and the potential of the less-positive half cell ... 

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