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Temperature coefficient cell potential

Contemplating then cell (3), ° if the Hg electrode does not contribute to the temperature coefficient ofthe potentials measured, then 3 of the cell (being equivalent to AS°) must yield here the entropy difference (hS - S +lof the ion undergoing a reversible equilibrium reaction at Pt (right-hand electrode, cell 3) with Hj in the gas phase and in solution at unit activity. [Pg.111]

Ideally a standard cell is constmcted simply and is characterized by a high constancy of emf, a low temperature coefficient of emf, and an emf close to one volt. The Weston cell, which uses a standard cadmium sulfate electrolyte and electrodes of cadmium amalgam and a paste of mercury and mercurous sulfate, essentially meets these conditions. The voltage of the cell is 1.0183 V at 20°C. The a-c Josephson effect, which relates the frequency of a superconducting oscillator to the potential difference between two superconducting components, is used by NIST to maintain the unit of emf. The definition of the volt, however, remains as the Q/A derivation described. [Pg.20]

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. [Pg.597]

These relationships can be used to obtain thermodynamic data otherwise difficult to get. Vice versa they can be used to calculate the temperature coefficient of a cell voltage respectively an electrode potential based on known thermodynamic data. [Pg.411]

This sharp decline in cell output at subzero temperatures is the combined consequence of the decreased capacity utilization and depressed cell potential at a given drain rate, and the possible causes have been attributed so far, under various conditions, to the retarded ion transport in bulk electrolyte solutions, ° ° - ° ° the increased resistance of the surface films at either the cathode/electrolyte inter-face506,507 Qj. anode/electrolyte interface, the resistance associated with charge-transfer processes at both cathode and anode interfaces, and the retarded diffusion coefficients of lithium ion in lithiated graphite anodes. - The efforts by different research teams have targeted those individual electrolyte-related properties to widen the temperature range of service for lithium ion cells. [Pg.151]

The overall rate of an electrochemical reaction is measured by the current flow through the cell. In order to make valid comparisons between different electrode systems, this current is expressed as cunent density,/, the current per unit area of electrode surface. Tire current density that can be achieved in an electrochemical cell is dependent on many factors. The rate constant of the initial electron transfer step depends on the working electrode potential, Tlie concentration of the substrate maintained at the electrode surface depends on the diffusion coefficient, which is temperature dependent, and the thickness of the diffusion layer, which depends on the stirring rate. Under experimental conditions, current density is dependent on substrate concentration, stirring rate, temperature and electrode potential. [Pg.4]

The configuration-bias Monte Carlo (CB-MC) technique (112) has also been extensively applied to characterize the sorption of alkanes, principally in silicalite (111, 156, 168-171) but also in other zeolites (172-174). Smit and Siepmann (111, 168) presented a thorough study of the energetics, location, and conformations of alkanes from n-butane to n-dodecane in silicalite at room temperature. A loading of infinite dilution was simulated, based on a united-atom model of the alkanes and a zeolite simulation box of 16 unit cells. Potential parameters were very similar to those used in the MD study of June et al. (85). As expected, the static properties (heat of adsorption, Henry s law coefficient) determined from the CB-MC simulations are therefore in close agreement with the values of June et al. The... [Pg.72]

All species are aqueous unless otherwise indicated. The reference state for amalgams is an infinitely dilute solution of the element in Hg. The temperature coefficient, dE°/dT, allows us to calculate the standard potential, E°(T), at temperature T E°(T) — Ec + (dE°/dT)AT. where A T is T — 298.15 K. Note the units mVIK for dE°ldT. Once you know E° for a net cell reaction at temperature T, you can find the equilibrium constant, K, for the reaction from the formula K — lOnFE°,RTln w, where n is the number of electrons in each half-reaction, F is the Faraday constant, and R is the gas constant. [Pg.725]

The standard electrode potential and its temperature coefficient are found in the literature.36 Kinetic parameter values were measured in-house for HOR,33 ORR,34 OER,35 and COR.12 22 Table 2 gives cell component materials and transport properties. The membrane and electrode proton conductivity in Table 2 are based on the measured membrane and electrode resistance,42,43 which is a strong function of relative humidity (RH). In what follows next, we will describe the... [Pg.53]

Calculate the free energy change (heat change) of the cell reaction (AH) in calories for two battery systems (a) A lead-acid cell with an open-circuit voltage of 2.01 V at 15 °C and a temperature coefficient of resistance (dE/dT) of 0.0037 V/K. (b) A Zn-Hg cell (Clark cell) with an open-circuit potential of 1.4324 V at 15 °C and a temperature coefficient of 0.00019 V/K. (Bhardwaj)... [Pg.379]

There are two other common versions of this half-cell the normal and tenth normal csAo-mel electrodes, in which the KCl concentration is either 1.0 or 0.1 N. The saturated electrode is the easiest to prepare and the most convenient to use but has the largest temperature coefficient. The half-cell potential for each of the calomel electrodes has a different value relative to the standard hydrogen electrode these emf valnes are given in Table 1. Calomel electrodes can be easily prepared in the laboratory and are also available commercially. Two typical calomel electrode designs are shown in Fig. 7. [Pg.609]

Electromotive force measurements of the cell Pt, H2 HBr(m), X% alcohol, Y% water AgBr-Ag were made at 25°, 35°, and 45°C in the following solvent systems (1) water, (2) water-ethanol (30%, 60%, 90%, 99% ethanol), (3) anhydrous ethanol, (4) water-tert-butanol (30%, 60%, 91% and 99% tert-butanol), and (5) anhydrous tert-butanol. Calculations of standard cell potential were made using the Debye-Huckel theory as extended by Gronwall, LaMer, and Sandved. Gibbs free energy, enthalpy, entropy changes, and mean ionic activity coefficients were calculated for each solvent mixture and temperature. Relationships of the stand-ard potentials and thermodynamic functons with respect to solvent compositions in the two mixed-solvent systems and the pure solvents were discussed. [Pg.354]

However, in 1941, Lee and Tai considered the potential and temperature coefficients of the following cells ... [Pg.111]

What of Lee and Tai s assumption that a charge-free surface involves no potential contribution to the cell In facL work done much later suggests that the missing temperature coefficient is only 0.01, so that the error Lee and Tai introduced by their outmoded assumption is indeed negligible. [Pg.112]

Two parts of the 1770 system are temperature sensitive. The chemistry itself, largely due to the volatility of iodine, has a substantial temperature coefficient, and the electrode response ean vary slightly when sample temperature differs from the temperature at which the electrode was calibrated. Since it is the sum of these components that is of practical interest, we examined the system temperature, after calibration at 25 °C, in an environmental chamber. Temperature was measured directly in the electrode flow cell, and potential of the electrode monitored using a digital millivolt meter. The results appear in Figure 5. Based on this information. [Pg.787]

Ni(OH)2 and NiOOH coexist in a single phase of a homogenous solid-state solution, and their relative concentration ratio in the solid solution varies with the state of charge (SOC) of the cell. Therefore, the cathode potential varies with the battery SOC governed by the Nernst equation. The temperature coefficient of the cathode reaction is about —0.5mV/°C. [Pg.1898]

Studies of Ax have been used to make estimates of the absolute value of, the surface potential at the interface between pure water and air. Since this quantity cannot be determined experimentally, such estimates necessarily involve an extrathermodynamic assumption. The most convincing evidence about the sign of and thus, the orientation of water at the interface, comes from experiments designed to study the temperature coefficient /dT. The cell used was... [Pg.415]

As stated earlier, the reference electrode in a cell used for electroanalysis is designed so that its potential is independent of the composition of the test solution. There are several general properties that reference electrodes should have in order to be useful in analysis (1) they should be reversible with an electrode potential which is independent of time and reproducible (2) they should have a small temperature coefficient (3) they should be ideally non-polarizable with negligible effects from the flow a small current through the system and (4) they should be easily constructed. The most commonly used reference electrodes are those based on on the mercury calomel system and the silver silver chloride system. The electrolyte most commonly used in these systems is KCl. Relevant parameters for commonly used reference electrodes are given in table 9.4. [Pg.475]

In view of the failure of the rigid sphere model to yield the correct isochoric temperature coefficient of the viscosity, the investigation of other less approximate models of the liquid state becomes desirable. In particular, a study making use of the Lennard-Jones and Devonshire cell theory of liquids28 would be of interest because it makes use of a realistic intermolecular potential function while retaining the essential simplicity of a single particle theory. The main task is to calculate the probability density of the molecule within its cell as perturbed by the steady-state transport process. [Pg.161]

Investigations of Braune and Koref.—We are indebted to Braune and Koref (77, and particularly 986) for an extremely careful and painstaking test of the application of the Heat Theorem to condensed systems. The test was made on a number of galvanic cells in exactly the same manner as that already employed by U. Fischer. In all the cells U was found to have nearly the same value, whether determined from the temperature coefficient of the potential or by direct thermochemical means this provides a guarantee that the cells under observation were actually controlled by the process assumed to be supplying the current, though as a matter of fact there was hardly any doubt of this in the cases examined. [Pg.118]

The quantity (d Th,m/dr) in the integral of Equation (26-36) is defined standard Seebeck coefficient and is a characteristic property of a glass-forming melt. It is determined by means of zirconia microelectrodes (Figure 26-14), which eliminate temperature-dependent redox potentials inherently included in the emf if platinum electrodes were applied to these measurements [12]. The cell scheme for measuring standard Seebeck coefficients according to Figure 26-14 is... [Pg.469]

If the cell does not contain a gas electrode, then since the entropy changes of reactions in solution are frequently rather small, less than 50 J/K, the temperature coefficient of the cell potential is usually of the order of 10 " or 10 V/K. As a consequence, if only routine equipment is being used to measure the cell potential and the temperature coefficient is sought, the measurements should cover as wide a range of temperature as is feasible. [Pg.382]

Through Eq. (17.42), the temperature coefficient of the cell potential yields the value of AS. From this and the value of i at any temperature we can calculate Aif for the cell reaction. Since Aif = AG -t- T AS, then... [Pg.383]

In Example 17.3, we computed the AH° for the cell reaction from the cell potential and its temperature coefficient. If the reaction were carried out irreversibly by simply mixing the reactants together, AH° is the heat that flows into the system in the transformation by the usual relation, AH = Qp. However, if the reaction is brought about reversibly in the cell, electrical work in the amount is produced. Then, by Eq. (9.4), the definition of AS,... [Pg.383]

The potential of this cell is very stable with a small temperature coefficient. The left half-cell (anode) reaction in the Weston cell is reversible to cadmium ions,... [Pg.50]

Still another approach is to make use of the temperature coefficient of an appropriate series of cell reactions. It is necessary to assume that the potential of the electrocapillary maximum corresponds to zero metal-solution potential difference. A recent modification suggested by Ikeda makes use of the Eastman thermocell as well as the temperature coefficient of the mobility of an ion. [Pg.282]


See other pages where Temperature coefficient cell potential is mentioned: [Pg.636]    [Pg.38]    [Pg.192]    [Pg.199]    [Pg.123]    [Pg.148]    [Pg.389]    [Pg.123]    [Pg.173]    [Pg.111]    [Pg.360]    [Pg.361]    [Pg.55]    [Pg.193]    [Pg.63]    [Pg.577]   
See also in sourсe #XX -- [ Pg.160 ]




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