Temperature scale operational definition

Each of these properties can provide the basis for an operational definition of a temperarnre scale. For example, the Celsius temperature is defined by Equation (3.1) ... 

Initial concepts of temperature came from the physical sensation of the relative hotness or coldness of bodies. This sensation of warmth or cold is so subjective relative to our immediate prior exposure that it is difficult to use for anything but simple qualitative comparison. The need to assign a quantitative value to temperature leads to the definition of a temperature scale. The concept of fixed points of temperature arises from the observation that there exist some systems in nature that always exhibit the same temperatures. The scientific or thermodynamic definition of temperature comes from Kelvin, who defined the ratio of the thermodynamic or absolute temperatures of two systems as being equal to the ratio of the heat added to the heat rejected for a reversible heat engine operated between the systems. This unique temperature scale requires only one fixed point, the triple point of water, for its definition. 

Thermodynamics and motion can be used as a base for an operational definition of the solid state. A solid is a phase below its glass- or melting-transition temperature where the molecular motion is almost completely restricted to small-amplitude vibrations. Both transitions are easily determined by thermal analysis (the operation). Recently it has become possible by simulation on supercomputers to establish the link from the microscopic thermal motion of macromolecules to the macroscopic thermal analysis. By solving the equation of motion, one can produce a detailed movie of molecular motion (see Sect 1.3.4, Fig. 1.47). At high temperature, conformational disorder is seen, i.e., the crystal can change to a condis state. Note that even the conformational motion occurs in a picosecond time scale (see Sect. 5.3.4). 

Temperature and thermometry are of fundamental importance in thermodynamics. Unlike the other physical quantities discussed in this chapter, temperature does not have a single unique definition. The chosen definition, whatever it may be, requires a temperature scale described by an operational method of measuring temperature values. For the scale to be useful, the values should increase monotonically with the increase of what we experience physiologically as the degree of hotness. We can define a satisfactory scale with any measuring method that satisfies this requirement. The values on a particular temperature scale correspond to a particular physical quantity and a particular temperature unit. 

The increasing use of heavy water (D2O) in studies of reaction mechanism, in nuclear technology and in medical research has created a demand for accurate measurements of acidity in this medium. As the glass electrode responds satisfactorily to deuterium ion in D2 O, this need is provided by modern pH meters. The operational definition of pH also allows the creation of a scale, the pD scale, where the solvent is heavy water. Reference values have been assigned to three selected buffers in heavy water (Paabo Bates, 1969). Standard pD values for these buffers for various temperatures are given in Table 6.8. When pH meters are standardized against these buffers in heavy water solution, the meter readings are in pD units. 

Definitions of many of the concepts and terms that underlie much of the chemical and process industries are summarized, such as unit operations and unit processes, to name a few. Design variables for sizing piping and process equipment are briefly presented. Systems of units, different temperature scales, and pressure scales are described. 

Electrolytic treatment technologies have definite advantages over these more common treatment processes. The primary benefit is that chemical change in an electrochemical process is brought about by the ability to add or remove electrons from species to be treated. This eliminates the use of redox agents to treat wastes and also removes the need to treat spent redox streams. Other, equally important, benefits of electrochemical processes include close control of reactions through control of the applied potential or current lower operating temperatures and hence lower costs increased possibility of on-site treatment, especially in small-scale use possible simultaneous use of the anode and cathode for waste minimization and the ability to... 

Vacuum tray driers offer an alternative method for drying small quantities of material. When scaled up, construction becomes massive to withstand the applied vacuum and cost is further increased by the associated vacuum equipment. Vacuum tray driers are, therefore, only used when a definite advantage over the hot air oven is secured, such as low temperature drying of thermolabile materials or the recovery of solvents from the bed. The exclusion of oxygen may also be advantageous or necessary in some operations. 

Tg can be defined operationally as the temperature at which the forces holding the distinct components of an amorphous solid together are overcome, so that these components become able to undergo large-scale molecular motions, limited mainly by the inherent resistance of each component to such flow. The practical effects of the glass transition on the processing and performance characteristics of polymers, as well as the key aspects of its physics, are implicit in this definition. 

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