Reality, chemical

Young, H. A., Young, B. A. (1976). Black doctorates Myth and reality. Chemical Technology, 6,... 

The simple model of bonds between atoms, reducing chemical bonding to formal atom pair interactions is unsatisfactory for many molecules, since it fails to represent the actual bonding in conjugated or aromatic systems. In reality, chemical bonding is a molecular property, not a property of atom pairs. 

On the other hand, it is assumed in the stationary theory of the thermal explosion, on which the F-K equation is based, that the term, dT dt, in Eq. (20) takes the value of zero, but the term, A T, takes a definite value. In other words, as stated in Section 1.3, it is assumed in the latter theory that the temperature of a solid (powdery, in reality) chemical of the TD type, including every gas-permeable oxidatively-heating substance, having an arbitrary shape and an arbitrary size, placed in the atmosphere maintained at a temperature situated below the critical state for the thermal explosion, does not vary with time as a whole, but there is a spatially gradient distribution of temperature in the chemical (see the F-K model in Fig. 3 in Section 1.5). It must, thus, be admitted that the spatial distribution of temperature in a powdery chemical of the TD type, placed in the atmosphere under isothermal conditions, is a gradient one even in the early stages of the self-heating process. 

In Chapter 3, a classification of self-heating chemicals, except gas-permeable oxidatively-heating substances, is introduced. Treatments of gas-permeable oxidatively-heating substances are made in Chapters 7 and 8. Self-heating chemicals are divided into two large groups, i.e., the thermal decomposition or TD type and the autocatalytic reaction or AC type. The TD type is subdivided into liquid chemicals, for each of which the Semenov equation is applied to calculate the Tc, and, solid (powdery, in reality) chemicals, for each of which the F-K equation is applied to calculate the Tc. On the other hand, the AC type is subdivided into high explosives of the true AC type and powdery chemicals of the quasi-AC type. 

In reality, chemical bonding is a molecular property, not a property of atomic... 

This will require a battery of diagnostic tools, which characterizes the patient in such a way that personalized treatment becomes a reality. Chemical biology will also make valuable contributions by dealing with the biological systems and supporting the development of new diagnostic tools. 

Toxins are poisons produced by living organisms which are then extracted or copied to produce militarily useful quantities. Naturally occurring toxins are technically biological weapons but are included here because they are in reality chemical weapons and are applied as chemicals rather than as living organisms such as germs, spiders, or vipers. 

However, until relatively recently, most workers concerned with waste management have tended to consider chemical processes primarily because they may affect the physical containment properties of engineered barrier systems. Several texts have examined these physical aspects of containment in considerable detail (e.g. Bentley 1996). Implicitly, there has been a tendency to view chemical containment as an aspect of physical containment. For example, any collapse of expandable clay minerals, such as may be caused by interactions involving polar organic molecules, will affect the physical integrity of clay barriers (e.g. Bowders Daniele 1987 Hettirachi et al. 1988). However, this view of containment is simplistic. In reality, chemical and physical processes must be considered holistically. For example, where clay is used to confine a waste, it should be considered as a physico-chemical barrier to contaminant migration (Horseman et al. 1996). 

In order to be realistic, environmental models must contain multiple phases, and are often referred to as multiphasic, or multimedia compartment models. Being so requires interfaces that separate the phases and media. These interfaces can be real or idealized (i.e., imaginary). Two-dimensional interface planes are assumed to exist between the air-water, water-sediment, and soil-air phases or media. In reality, chemical transport across the air-water interphase plane involves a true phase change. The watery interface plane at the water-bed sediment junction and airy interface plane at the soil-air junction are only separated by imaginary planer surfaces. Nevertheless, due to the dramatic changes that typically occur within the fluid and the associated media fluid dynamics on either interface side, different transport processes occur on opposite sides, typically. Therefore it is also practical to define an interfacial compartment for such imaginary and idealized interface situations. The interfacial compartment concept for multimedia, interphase chemical transport is based on the following ideas ... 

Both plastics and steel are man-made, but that does not make them unnatural. They are made from elements found in nature, by people who as carbon-based life forms are not only part of nature, but have been working with natural elements and modifying those elements since early hominids walked the earth. Just as a metals expert constructs and alters metals, so does a polymer chemist synthesize compounds from organic elements. In reality, chemicals and synthetics are a result of a creative process—or, in other words, people making stuff. 

Combining informativeness and accuracy with readability, Stephanie Yanchinski explores the hopes, fears and, more importantly, the realities of biotechnology - the science of using micro-organisms to manufacture chemicals, drugs, fuel and food. 

It is useful, nevertheless, to bring to mind their composition and their means of action (Goodacre, 1958). Several components of the same family can in reality be utilized tetraethyl lead, Pb ( 2115)4 or TEL, tetramethyl lead, Pb (CHg) or TML, mixtures of these products or yet mixed chemical components including various combinations of the groups C2Hg and CH3 Pb ( 2115)2 ( 113)2, Pb ( 2115)3 113, Pb ( 2Hg) ( 113)3. 

To avoid these problems, refiners commonly use additives called detergents" (Hall et al., 1976), (Bert et al., 1983). These are in reality surfactants made from molecules having hydrocarbon chains long enough to ensure their solubility in the fuel and a polar group that enables them to be absorbed on the walls and prevent deposits from sticking. The most effective chemical structures are succinimides, imides, and fatty acid amines. The required dosages are between 500 and 1000 ppm of active material. 

Burger M T, A Armstrong, F Guamieri, D Q McDonald and W C Still 1994. Free Energy Calculations in Molecular Design Predictions by Theory and Reality by Experiment with Enantioselective Podand lonophores. Journal of the American Chemical Society 116 3593-3594. 

This discussion may well leave one wondering what role reality plays in computation chemistry. Only some things are known exactly. For example, the quantum mechanical description of the hydrogen atom matches the observed spectrum as accurately as any experiment ever done. If an approximation is used, one must ask how accurate an answer should be. Computations of the energetics of molecules and reactions often attempt to attain what is called chemical accuracy, meaning an error of less than about 1 kcal/mol. This is suf-hcient to describe van der Waals interactions, the weakest interaction considered to affect most chemistry. Most chemists have no use for answers more accurate than this. 

Historically carbohydrates were once considered to be hydrates of carbon because their molecular formulas m many (but not all) cases correspond to C (H20) j It IS more realistic to define a carbohydrate as a polyhydroxy aldehyde or polyhydroxy ketone a point of view closer to structural reality and more suggestive of chemical reactivity... 

Reality suggests that a quantum dynamics rather than classical dynamics computation on the surface would be desirable, but much of chemistry is expected to be explainable with classical mechanics only, having derived a potential energy surface with quantum mechanics. This is because we are now only interested in the motion of atoms rather than electrons. Since atoms are much heavier than electrons it is possible to treat their motion classically. Quantum scattering approaches for small systems are available now, but most chemical phenomena is still treated by a classical approach. A chemical reaction or interaction is a classical trajectory on a potential surface. Such treatments leave out phenomena such as tunneling but are still the state of the art in much of computational chemistry. 

There are no available data to establish whether nonconductive, low viscosity chemical products such as ethyl ether similarly display hyperbolic relaxation below about 2 pS/m, or even whether this phenomenon is a practical reality for such liquids. Should Ohmic relaxation behavior continue to much less than 0.5 pS/m the risk of static accumulation would be enhanced compared with petroleum distillates. 

Absorption, distribution, biotransformation, and excretion of chemical compounds have been discussed as separate phenomena. In reality all these processes occur simultaneously, and are integrated processes, i.e., they all affect each other. In order to understand the movements of chemicals in the body, and for the delineation of the duration of action of a chemical m the organism, it is important to be able to quantify these toxicokinetic phases. For this purpose various models are used, of which the most widely utilized are the one-compartment, two-compartment, and various physiologically based pharmacokinetic models. These models resemble models used in ventilation engineering to characterize air exchange. 

The chemical reactions that occnr in flames transform an initial reactant mixtnre into final reaction prodncts. In the case of fnel-oxygen combns-tion, the final prodncts are principally water vapor and carbon dioxide, althongh nnmerons other prodncts snch as carbon monoxide may be formed, depending on the reactant composition and other factors. If the ratio of fnel-to-oxygen is stoichiometric, the final reaction prodncts, by definition, contain no excess fnel or oxygen. Theoretically, this means that partial oxidation prodncts snch as CO (itself a fnel) are not formed. In reality, partial oxidation prodncts snch as CO or OH are formed by high tem-peratnre reactions. For example, the molar stoichiometric reaction of methane is written ... 

Reality Check In ordinary chemical reactions, the energy change is of the order of 50 kj/g or less. In this nuclear reaction, the energy change is much, much greater... 

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