Temperature coefficient definition

The temperature compensator on a pH meter varies the instrument definition of a pH unit from 54.20 mV at 0°C to perhaps 66.10 mV at 60°C. This permits one to measure the pH of the sample (and reference buffer standard) at its actual temperature and thus avoid error due to dissociation equilibria and to junction potentials which have significant temperature coefficients. 

There is no discontinuity in volume, among other variables, at the Curie point, but there is a change in temperature coefficient of V, as evidenced by a change in slope. To understand why this is called a second-order transition, we begin by recalling the definitions of some basic physical properties of matter ... 

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. 

It will be seen that ions which have an unusually high mobility have, at the same time, an abnormally low temperature coefficient for the mobility. The points in the diagram make a definite pattern, the values... 

Thus, two interpretations based on two different concepts of the effect of temperature on dipole orientation have been put forward. The two views clash with each other on physical as well as chemical grounds. However, the view based on the correlation of Fig. 25 introduces chemical concepts that are absent in the other, which ignores some definite facts. For instance, although a value for dEa=0/dT is not available for Ga, the temperature coefficient of C is apparently small.905 Ga is universally recognized as a strongly hydrophilic metal. Therefore, according to the simple model of up-and-down dipoles, the effect of temperature should be major, which is in fact not the case. 

Fig. 101.—Experimental and theoretical (dashed line) stress-strain curves for tetra-linked polyamide with y/V) X10 = 1.34 at low elongations. Temperatures (in °C) were 229° 241° O 253° 281° 3. The range is too small to show a definite temperature coefficient beyond the experimental error. (Schaefgen and Flory. )...

As equation 2.4.8 indicates, the equilibrium constant for a reaction is determined by the temperature and the standard Gibbs free energy change (AG°) for the process. The latter quantity in turn depends on temperature, the definitions of the standard states of the various components, and the stoichiometric coefficients of these species. Consequently, in assigning a numerical value to an equilibrium constant, one must be careful to specify the three parameters mentioned above in order to give meaning to this value. Once one has thus specified the point of reference, this value may be used to calculate the equilibrium composition of the mixture in the manner described in Sections 2.6 to 2.9. 

Thermistor basedflow-through calorimetric sensors. Enzyme thermistors make the most widely developed type of heat measurement-based sensors. The thermistors are normally used as temperature transducers in these devices. Thermistors are resistors with a very high negative temperature coefficient of resistance. They are ceramic semiconductors made by sintering mixtures of metal (manganese, nickel, cobalt, copper, iron) oxides. Like the two previous groups, thermistor sensors do not comply strictly with the definition of "sensor" as they do not consist of transducers surrounded by an immobilized enzyme rather, they use a thermistor at the end of a small... 

A direct numerical relationship between heat and momentum fluxes, as for the simple Reynolds analogy for a single phase, is not obtained in this case because of a basic and significant difference in heat transfer coefficient definitions. For singlephase flow in pipes, the mixed mean or integrated average temperature is used in... 

The detection of sharp plasmon absorption signifies the onset of metallic character. This phenomenon occurs in the presence of a conduction band intersected by the Fermi level, which enables electron-hole pairs of all energies, no matter how small, to be excited. A metal, of course, conducts current electrically and its resistivity has a positive temperature coefficient. On the basis of these definitions, aqueous 5-10 nm colloidal silver particles, in the millimolar concentration range, can be considered to be metallic. Smaller particles in the 100-A > D > 20-A size domain, which exhibit absorption spectra blue-shifted from the plasmon band (Fig. 80), have been suggested to be quasi-metallic [513] these particles are size-quantized [8-11]. Still smaller particles, having distinct absorption bands in the ultraviolet region, are non-metallic silver clusters. 

Another example often quoted is that there is no sample effect when measuring the length of a table. First, this is an incomplete definition of a measurand, since it is not clear what is meant by the length. But if, for example, the table forms a part of a measuring system to measure the precise shape of objects then the shape of the table can have an influence on the result. Then such factors as the material of the table, its temperature coefficient, the temperature gradients across the table, the loading of the table, the friction between its feet and the floor are sample effects that need to be taken into account. 

If, then, we are to explain the temperature variation of fx by means of this process of gradual uncoupling, definite relationships must hold between the absolute magnitude of the moment (as compared with the value for the ideally uncoupled state) and its temperature coefficient. This very point would seem to lead to difficulties in connexion with the results of Werner which we mentioned above. In the ideally uncoupled state quinol diethyl ether should have the moment V 2fx, where for fx the value for phenetole (i o. should be inserted. In this way we obtain 1 4. io as the limiting value for the ideally uncoupled state, i.e. a number which is smaller than the moment obtained experimentally for the di-derivative (i 7.10 at 20° C.). Now with rising temperature Werner does not obtain the anticipated tendency towards the limiting value but a... 

We now turn to the numerous observations made on the activated adsorption of hydrogen on reduced copper. In this case a definite, large temperature coefficient or activation energy Ae has been found. It was calculated by the conventional formula... 

The reproducibility of the effective mobility is governed by temperature and pH effects. An acceptable run-to-run pH reproducibility can usually be assured, at least in equipment where the effects of possible electrode reactions can be avoided. Again, temperature plays a leading role The effective mobility has a temperature coefficient of 2-3% per degree. Most buffer solutions, incidentally, have a temperature-dependent pH value, so that changing the temperature in the capillary will, for weak ions, even lead to changing degrees of dissociation and, hence, effective mobility. These effects are, by definition, different for different buffers and different sample components. 

Ionic mobilities generally have a temperature coefficient of around -i-2.5%/degree, but it is not exactly the same for all ions. Incidentally, water viscosity has a temperature coefficient of approximately -2.5%/degree. This sometimes leads to the erroneous conclusion that ionic mobility is, by definition, inversely proportional to liquid viscosity, which is an oversimplification, originating also from the following relationship ... 

Present the definitions of biogeochemical uptake coefficient, active temperature coefficient and relative biogeochemical cycling coefficient, and give examples of these coefficients for various ecosystems. 

The following reasoning shows also how inconvenient is the introduction of the temperature coefficient at constant volume if we warm a cell at constant volume, the pressure increase, and thus also the E.M.F., is definitely fixed only if we know, in addition to the coefficients of thermal expansion of the cell components, the proportions also in which they are present the E.M.F. measured at constant pressure is, however, independent of the proportions of the separate phases. This fact again shows that equation (157) is of a form which cannot usually be employed in practice. 

On the contrary, with Daoud and Jannink,49 we can consider the length of the polymers as fixed and assume that the temperature and consequently the solubility of the solution may vary. In this case, a polymer solution is represented by a point in the (C, T) plane. The good-solubility domain corresponds to temperatures T > TF where Tr in the Flory temperature. By definition TrF(N) is the temperature at which the second virial coefficient vanishes and TF = lim Trf (N - qo ). Anyway, if N is large TrF(N) is close to TF. 

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,... 

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