Absolute or Kelvin

Knowledge of the numerical value of the entity represented by Eq. (9.1) allows one to make up cells that give the potential of an electrode "on the absolute scale, just as the Celsius scale was later shown to be expressed on the absolute or Kelvin scale of temperatures, in which there is a rationally based zero at -273 °C. Thus, to find the absolute value, VM>abs of an electrode potential expressed on the standard hydrogen scale, one writes... 

As you can see from Figure 11.19 on page 442, the volume of a gas increases or decreases by a fixed increment when subjected to a change in temperature. The algebraic statement of Charles law depends on using absolute, or Kelvin, temperatures. This law is stated as V a T, where T is measured in kelvins. (Figure 11.18 uses Charles law to explain how a thermometer works.)... 

Still another temperature scale used in the sciences is the absolute or Kelvin scale. On this scale water freezes at 273 K and boils at 373 K. On the Kelvin scale, the unit of temperature is called a kelvin and is symbolized by K. Thus, on the three scales, the boiling point of water is stated as 212 Fahrenheit degrees (212 °F), 100. Celsius degrees (100. 

Remember that all equations in thermodynamics use the absolute or kelvin temperature scale, so that if you are given temperatures in °C, you must convert them to the kelvin scale before using them. The standard temperature of 25 °C for example is 298.15 K. 

The basic temperature scale is the absolute or Kelvin scale. The absolute zero of temperature is the lowest temperature theoretically possible, and is so low that the scale cannot be used conveniently in chemical processing. Therefore, in practice, we use the centigrade (now called Celsius) and less frequently the Fahrenheit scales. These scales utilize fixed points, which are normally the freezing point and boiling point of pure water. Thus we have ... 

Correlated color temperature Term used to describe the color of white light sources. Specifically, it is the temperature of the Planckian (black body) radiator, which produces the chromaticity most similar to that produced by the light source in question. The temperature is expressed in degrees on the absolute or Kelvin scale, or in mireds (micro-reciprocal degrees), 10 /T. See color temperature. 

Thomson, wniiam, 1st Baron Kelvin (1824-1907) Irish-born Scottish physicist and mathematician who proposed the absolute, or Kelvin, temperature scale (1848) and, at around the same time as Rudolf Clausius, established the second law of thermodynamics. He also invented a tide predictor and a harmonic analyzer. 

Carnot s research also made a major contribution to the second law of thermodynamics. Since the maximum efficiency of a Carnot engine is given by 1 -T( H, if the engine is to be 100 percent efficient (i.e., Cma = 1), Tc must equal zero. This led William Thomson (Lord Kelvin) to propose in 1848 that Tf must be the absolute zero of the temperature scale later known as the absolute scale or Kelvin scale. ... 

T(hot) is the temperature on the hot side of the engine. T(cold) is the temperature on the cold side of the engine. These temperatures must be measured in absolute degrees (Kelvin or Rankine). 

Temperature Scales A quantitative description of temperature requires the definition of a temperature scale. The two most commonly encountered in thermodynamics are the absolute or ideal gas (°A) scale and the thermodynamic or Kelvin (K) scale."... 

The Thermodynamic or Kelvin Temperature Scale Description of the Kelvin temperature scale must wait for the laws of thermodynamics. We will see that the Kelvin temperature is linearly related to the absolute or ideal gas temperature, even though the basic premises leading to the scales are very different, so that... 

In the next chapter, we will return to the Carnot cycle, describe it quantitatively for an ideal gas with constant heat capacity as the working fluid in the engine, and show that the thermodynamic temperature defined through equation (2.34) or (2.35) is proportional to the absolute temperature, defined through the ideal gas equation pVm = RT. The proportionality constant between the two scales can be set equal to one, so that temperatures on the two scales are the same. That is, 7 °Absolute) = T(Kelvin).r... 

The difference is that the temperature in equation (3.85) is the absolute or ideal gas temperature, while the temperature in equation (2.82) is the thermodynamic or Kelvin temperature. The conclusion we reach when comparing the two equations is that the absolute and Kelvin temperatures must be proportional to one another. That is... 

This means that all substances have some entropy (dispersal of energy and/or matter, i.e. disorder) except when the substance is a pure, perfect, motionless, vibrationless crystal at absolute zero Kelvin. This also implies that the entropy of a substance can be expressed on an absolute basis. 

Absolute zero. Minus 273°C or minus 460 or 0°K or Kelvin, the scale used in theoretical physics and chemistry. Absolute zero is the theoretical temperature at which all molecular activity ceases. In practical terms, the lowest reachable temperature is about 1°K. 

The rate of radiant thermal energy transfer between two bodies is described by the Stefan-Boltzmann law. Originally proposed in 1879 by Joseph Stefan and verified in 1884 by Ludwig Boltzmann, the Stefan-Boltzmann law states thatthe emission of thermal radiative energy is proportional to the fourth power of the absolute temperature (Kelvin or Rankine) ... 

The SI unit of temperature is so defined that 0 K is the absolute zero of temperature. The SI or Kelvin scale is often called the absolute temperature scale. Although absolute zero does not appear to be attainable, it has been approached to within 10-4 K. 

The Planck theory of blackbody radiation provides a first approximation to the spectral distribution, or intensity as a function of wavelength, for the sun. The black-body theory is based upon a "perfect" radiator with a uniform composition, and states that the spectral distribution of energy is a strong function of wavelength and is pro portional to the temperature (in units of absolute temperature, or Kelvin), and several fundamental constants. Spectral radiant exitance (radiant flux per unit area) is de fined as ... 

The meaning of temperature in relation to molecular motion. The absolute zero of temperature. The Absolute scale or Kelvin scale. 

Temperature may be defined as that property of a body which determines the flow of heat. Two bodies are at the same temperature if there is no transfer of heat when they are placed together. Temperature is an independent dimension which cannot be defined in terms of mass, length, and time. The SI unit of temperature is the kelvin, and 1 kelvin (K) is defined as 1/273.16 times the triple point temperature. The triple point is the temperature at which water coexists in equilibrium with ice at the pressure exerted by water vapor only. The triple point is 0.01 K above the normal freezing point of water, at which water and ice coexist in equilibrium with air at standard atmospheric pressure. The SI unit of temperature is so defined that 0 K is the absolute zero of temperature the SI or Kelvin scale is often called the absolute temperature scale. Although absolute zero is never actually attainable, it has been approached to within 10" K. 

Equation (2.6) defines a new temperature scale, called a gas scale of temperature or, more exactly, an ideal gas scale of temperature. The importance of this scale lies in the fact that the limiting value of Kq, and consequently I/kq, has the same value for all gases. On the other hand, o does depend on the scale of temperature used originally for t. If t is in degrees Celsius (symbol °C), then 1/ao = 273.15 °C. The resulting T-scale is numerically identical to the thermodynamic temperature scale, which we will discuss in detail in Chapter 8. The SI unit of thermodynamic temperature is the kelvin (symbol K). Temperatures on the thermodynamic scale are frequently called absolute temperatures or kelvin temperatures. According to Eq. (2.6) (see also Appendix III, Sect. A-III-6),... 

Fortunately, there is a way out of this predicament. Using the second law of thermodynamics it is possible to establish a temperature scale that is independent of the particular properties of any substance, real or hypothetical. This scale is the absolute, or the thermodynamic, temperature scale, also called the Kelvin scale after Lord Kelvin, who first demonstrated the possibility of establishing such a scale. By choosing the same size degree, and with the usual definition of the mole of substance, the Kelvin scale and the ideal gas scale become numerically identical. The fact of this identity does not destroy the more fundamental character of the Kelvin scale. We establish this identity because of the convenience of the ideal gas scale compared with other possible scales of temperature. 

The absolute temperature T defined by Eq. (1-12) is of fundamental importance in thermodynamics. It appears again in the discussion of the second law of thermodynamics. The constant To can be determined experimentally from the limiting value of a as p approaches zero. The value To = 273.16 degrees centigrade (°C) has been obtained. By international convention the value of To is now arbitrarily fixed. The absolute temperature is measured in degrees absolute or degrees Kelvin (°K). The scale unit is the same as that for the centigrade scale. Thus 0°K corresponds to -273.16°C and 0°C corresponds to 273.16°K. 

Lord Kelvin stated that to measure is to know (Unnamed 2011). In fact, it would be more precise to say that to measure is to know... better. Almost all measurements have errors with respect to their absolute value, be it temperature, pressure, flow rate, or any of several other standard measurements necessary to evaluate a phenomenon, characterize an instrument, or run a chemical plant. Error is deflned as the absolute or relative difference between the measured value and the true value as measured by a recognized standard. Note that the term recognized standard is mentioned, and not true value since the true value can rarely, if ever, be known exactly. 

---