Term absorption

The more highly complexed hydrates of calcium chloride (CaCl2 nH2 O where n > 2) may also exhibit the characteristics of a Class 2 dryiag agent, because the hydrated species can physically absorb additional water to form a saturated solution. The term absorption is used to describe the phenomenon that occurs when a gas or vapor penetrates the soHd stmcture to produce a saturated solution ... 

In comparing the radiative properties of materials to those of a blackbody, fhe terms absorptivity and emissivity are used. Absorptivity is the amount of radiant energy absorbed as a fraction of the total amount that falls on the object. Absorptivity depends on both frequency and temperature for a blackbody if is 1. Emissivity is the ratio of the energy emitted by an object to that of a blackbody at the same temperature. It depends on both the properties of fhe subsfance and the frequency. Kirchhoff s law states that for any substance, its emissivity at a given wavelength and temperature equals its absorptivity. Note that the absorptivity and emissivity of a given substance may be quite variable for different frequencies. 

The term absorption is used whenever ions or other solutes are taken up by an ion exchanger. It does not imply any specific types of forces responsible for this uptake. 

When the component j can exist in both phases (e.g., the electrolyte and the electrode) it will undergo redistribution after the phases have come into contact, and in particular, some of it will be transferred into the interior of the phase, where none of it had existed previously. In this case the term absorption (or bulk uptake) is used for the component. 

Radiosity J Total thermal radiation energy leaving a surface (emitted and reflected) per unit time per unit area of energy transfer per unit area). The three terms, Absorptivity (a), Reflectivity (p), and Transmissivity (x), are all surface properties... 

As most drugs are preferably given orally, absorption which is complete, consistent and predictable is desirable. Although it may be possible from solubility, lipophilicity, pKa, molecular size, and animal data to make some prediction about likely absorption, only a study in humans will give quantitative data as the mechanisms of drug absorption are complex and still incompletely understood (Washington et al., 2001). It may be helpful here to distinguish between the terms absorption and bioavailability. ... 

We note here the similarity between the terms absorptance and absorbance. The latter is frequently employed in chemical infrared spectroscopy to denote logi0[l/T(x)], and may also be called optical density. As discussed in Section I.E.2, absorbance may not be directly employed in the convolution relation for instrumental spreading. 

Since the absorbance, A, is derived from a ratio (-log /// ), it is unitless. The term E, which is a proportionality constant, defines the efficiency or extent of absorption. If this is defined for a particular chromophore at a specific wavelength, the term absorption coefficient or absorptivity is used. However, students should be aware that in the older biochemical literature, the term extinction coefficient is often used. The units of E depend on the units of l (usually cm) and c (usually molar) in Equation 5.4. For biomolecules, E is often used in the form molar absorption coefficient, e, which is defined as the absorbance of a 1 M solution of pure absorbing material in a 1-cm cell under specified conditions of wavelength and solvent. The units of e are M l cm-1. To illustrate the use of Equation 5.4, consider the following calculation. 

The radiation may be due to emissions from a hot source, or to the luminescence, fluorescence or phosphorescence of the sample. An emission spectrum consists of a number of generally very narrow peaks (called spectral lines) occurring at certain wavelengths which are characteristic of the materials contained within the source. The amplitudes of the peaks are related to the abundance or concentration of the materials present. Alternatively, radiation from a source is passed through a sample. In this case the quantity absorbed by the sample at a particular wavelength is again characteristic of the materials present in the sample. This is termed absorption spectrometry and produces spectral transmission lines in the form of equally narrow valleys—or peaks (Fig. 6.42) where the information is expressed in terms of absorbance (si) rather than transmittance (20<57>, and ... 

The term absorption refers to the rate and extent to which an administered dose of a drug is taken into the body. In the case of oral administration, interest lies with the rate and extent of systemic absorption from the gastrointestinal tract following administration. If a drug is taken into the intestinal cells, it is deemed to have been absorbed, regardless of the extent to which it is metabolized. In contrast, the term bioavailability refers to the proportion of an administered dose that reaches the systemic circulation unchanged. 

We begin by defining two important terms absorption and adsorption. The International Union of Pure and Applied Chemistry offers precise definitions for absorption and adsorption (IUPAC, 1972). Absorption is used to describe a process where a component is transferred from one phase to another. Hydrogen gas can be absorbed by LaNis (Jurczyk, 2003). Adsorption is used to describe the increased or decreased concentration of a component at an interface. Water molecules will adsorb to an aluminum oxide surface (Al-Abadleh and Grassian, 2003). The concentration of water molecules on the aluminum oxide surface will be greater than the vapor phase, shown schematically in Figure 3.3. 

When the molecules of the adsorptive penetrate the surface layer and enter the structure of the bulk solid, the term absorption is used. It is sometimes difficult, impossible or irrelevant to distinguish between adsorption and absorption it is then convenient to use the wider term sorption which embraces both phenomena and to use the derived terms sorbent, sorbate and sorptive. 

The term absorptivity is synonymous with extinction coefficient, absorbancy index, and specific extinction (Browning 1967). 

Considering the two source terms (emission and in-scattering) and the two sink terms (absorption and out-scattering) defined on the right-hand side of the previous expression, one can transform the preceding fimdamental law in a more formal mathematical definition ... 

In acoustic terms, absorption can be expressed as aA while in modulus terms, absorption can be expressed as tan S. Using an approximation (for small tan S) that is almost always good to 1%, Ferry (2) points out that... 

The transport of the products of digestion into gut epithelial cells and from there to the portal blood is termed absorption. The absorption of some nutrients is passive while others require active transport. 

Adsorption is primarily a surface phenomenon, but it is often accompanied by a deeper penetration of the vapor or solute into the body of the solid adsorbent. This deeper penetration is akin to the formation of a solid solution and is termed absorption. Since it is seldom practicable to distinguish clearly between absorption and adsorption, McBain8 suggested the use of the broader term sorption to cover both phenomena. 

Movement up the ladder of energy levels (an upward transition) is only possible if the molecule or atom absorbs a photon whose energy exactly equcds the energy gap (A ) involved in the jump. (This requirement is called the Bohr condition.) This process (termed absorption) is shown in Fig. 20.3. During absorption, the photon vanishes. The relationship between the energy jump and the frequency of the absorbed light is... 

The term absorption is a generalization of extraction that can involve different phases (gas-liquid instead of liquid-liquid). However, the ideas are still the same. 

Whenever individual gas components are removed from gas mixes by means of a wash liquor (absorbent), this is termed absorption. Absorption processes range from physical processes to processes where absorption is of a purely chemical natiue. Between these two extreme cases, there are a number of processes using a mixture of physical and chemical effects. 

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