Chemicals substance definitions

In 1814, J.J. Berzelius succeeded for the first time in systematically naming chemical substances by building on the results of quantitative analyses and on the definition of the term "element by Lavoisier. In the 19th century, the number of known chemical compounds increased so rapidly that it became essential to classify them, to avoid a complete chaos of trivial names (see Section 2.2.4). 

Servos gives a beautifully clear explanation of the subject-matter of physical chemistry, as Ostwald pursued it. Another excellent recent book on the evolution of physical chemistry, by Laidler (1993) is more guarded in its attempts at definition. He says that it can be defined as that part of chemistry that is done using the methods of physics, or that part of physics that is concerned with chemistry, i.e., with specific chemical substances , and goes on to say that it cannot be precisely defined, but that he can recognise it when he sees it Laidler s attempt at a definition is not entirely satisfactory, since Ostwald s objective was to get away from insights which were specific to individual substances and to attempt to establish laws which were general. 

CRS provides information on chemical substances and how they are represented in the Environmental Protection Agency regulations and data systems. A search engine for chemicals by CAS number, name, molecular formula, chemical type, definition, or other data identifiers. 

Terminology The International Standards Organization has recently defined a corrosion inhibitor as a chemical substance which decreases the corrosion rate when present in the corrosion system at a suitable concentration, without significantly changing the concentration of any other corrosive agent. This last point is significant since it excludes chemicals employed for deaeration or pH control from the definition of a corrosion inhibitor. On the other hand, it should be noted that the inhibitor is .. . present in the corrosion system. . . , and thus arsenic when added to brasses to prevent dezin-cihcation may be classified as an inhibitor. 

In 1923. Lewis published a classic book (later reprinted by Dover Publications) titled Valence and the Structure of Atoms and Molecules. Here, in Lewis s characteristically lucid style, we find many of the basic principles of covalent bonding discussed in this chapter. Included are electron-dot structures, the octet rule, and the concept of electronegativity. Here too is the Lewis definition of acids and bases (Chapter 15). That same year, Lewis published with Merle Randall a text called Thermodynamics and the Free Energy of Chemical Substances. Today, a revised edition of that text is still used in graduate courses in chemistry. 

First, of all, I would like to clarify the term "new chemicals." I am referring to the TSCA definition as those chemicals not listed on the TSCA Chemical Substance Inventory and maintained on a daily basis by the Office of Toxic Substances within EPA. This is a list of all commercial chemicals - some 55,000 in all - produced in or imported into the United States during the period of 1975 through 1979. My talk this afternoon will not cover the thousands of formula changes in mixtures of chemicals which occur almost daily as industry tries to meet changing market demands. 

Environment As mentioned previously, a chemical product has to be produced for a particular function. Its existence is determined in the presence of the environment that it interacts with. This is to say, different from a chemical substance, the chemical product needs an environment to be defined. There is no empty space there must be a system and an environment. Therefore, this environment also needs a definition, which is established in the application field, and market for a particular chemical product. 

This chapter has attempted to analyze the nature of a chemical product. It is an entity with different chemical substances, manufactured for one or more applications. Along with other descriptions and definitions, this promotes an understanding of how the product is formed, its organization, and how it interacts with the environment. 

It is, of course, not necessary to have an extensive list of heats of reaction to determine the heat absorbed or evolved in every possible chemical reaction. A more convenient and logical procedure is to list the standard heats of formation of chemical substances. The standard heat of formation is the enthalpy of a substance in its standard state referred to its elements in their standard states at the same temperature. From this definition it is obvious that heats of formation of the elements in their standard states are zero. 

For a defence of the view that chemical substances may be regarded as energy-complexes, and that this view is equally as valid as the older notion of a chemical substance as an inertia-complex, i.e., as something made vp entirely of different units or atoms each characterised by the possession of a definite and constant weight at a fixed point on the earth s surface, see an article by the present writer, entitled "The Claims of Thermochemistry," Knowledge and Scientific News, vol. vii. (New Series), pp. 227 et seq. (July, 1910). 

In terms of waste definition, there are three basic approaches (as it pertains to petroleum, petroleum products, and nonpetroleum chemicals) to defining petroleum or a petroleum product as hazardous (1) a qualitative description of the waste by origin, type, and constituents (2) classification by characteristics based on testing procedures and (3) classification as a result of the concentraUon of specific chemical substances. 

As used in the act, the term chemical substance means any organic or inorganic substance of a particular molecular identity, including any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature and any element or uncombined radical. Items not considered chemical substances are listed in the definition section of the act. The term mixture means any combination of two or more chemical substances if the combination does not occur in nature and is not, in whole or in part, the result of a chemical reaction except that such term does include any combination that occurs, in whole or in part, as a result of a chemical reaction if none of the chemical substances comprising the combination is a new chemical substance and if the combination could have been manufactured for commercial purposes without a chemical reaction at the time the chemical substances comprising the combination were combined. 

In snmmary, many of the specific chemicals in petroleum are hazardous because of their chemical reactivity, fire hazard, toxicity, and other properties. In fact, a simple definition of a hazardons chemical (or hazardous waste) is that it is a chemical substance (or chemical waste) that has been inadvertently released, discarded, abandoned, neglected, or designated as a waste material and has the potential to be detrimental to the environment. Alternatively, a hazardons chemical may be a chemical that may interact with other (chemical) snbstances to give a prodnct that is hazardous to the environment. Whatever the case, methods of analysis mnst be available to determine the nnrture of the released chemical (waste) and from the data predict the potential hazard to the environment. 

In discussing gas phase separations, a few definitions will help in understanding the subject matter. Adsorbents, sometimes referred to here as sorbents, are solid chemical substances that possess micro-porous surfaces that can admit molecules to the interior surface of the structure. Zeolites in particular are solid, micro-porous, alumino-silicates with adsorption and or ion exchange capability. They affect separations by adsorbing molecules into their micro-structures. 

These two definitions reflect two sides of the same situation. In this book, the term critical effect(s) will be used for the hazard/effect considered as being the essential one(s) for the purpose of the risk characterization, e.g., for the establishment of a health-based guidance value, permissible exposure level, or Reference Dose. It should be noted that the critical effect could be a local as well as a systemic effect. It should also be recognized that the critical effect for the establishment of a tolerable exposure level is not necessarily the most severe effect of the chemical substance. For example, although a substance may cause a serious effect such as liver necrosis, the critical effect for the establishment of, e.g., an occupational exposure limit could be a less serious effect such as respiratory tract irritation, because the irritation occurs at a lower exposure level. 

In the OECD document Harmonised integrated classification system for human health and environmental hazards of chemical substances and mixtures (OECD 2001b), the following definitions are provided. 

The ultimate toxicological response following exposure to a chemical substance is most commonly the result of the action of this substance on a definite site or receptor. For a given concentration of the agent at the target site, the intensity of the response will depend on the quality of the action (the intrinsic activity) and the affinity of the compound for the receptor. 

A further aid in the location of the solvents and their exact specification is the Chemical Abstracts (CAS) Registry Number, shown in the second column. The Chemical Abstracts name may be the same as the commonly used one or may differ from it considerably, so that it is not always easy to find the solvents in these Chemical Substance Indexes of the Chemical Abstracts. Eor instance, benzene, methyl is a fairly transparent name for toluene, and methanol, phenyl a slightly less one for benzyl alcohol, but one has to become familiar with the systematics of Chemical Abstracts nomenclature in order to search for diethyl ether or any other more complicated compound. It is expected that with all this information available in table Al the solvents listed are definitely specified and readily found in the Abstracts and other compilation of information and data. 

The definition of result owed by the debtor What is the "benefit of a chemical substance" and how can be proven that the supplier has made available the benefit to the user. For this definition exact knowledge about the plant and the process in which the chemical substance is used is required. 

Berzelius introduced the term catalysis as early as 1836 to explain various decomposition and transformation reactions. He later referred to the special power that some substances (catalysts) have for influencing the affinity of chemical substances. According to the Ostwald definition of catalyst (1895), it was assumed that the catalyst remained unchanged in the course of the reaction but now it is known that it is involved in chemical bonding with the reactants during the catalytic cycle. Thus, catalysis is a process in which the rate of a reaction is enhanced under... 

As molecular orbital theory evolved over the years, several variations of Langmuir s definition of isosterism were expressed by others these are discussed in more recent publications [68, 69]. Burger s definition [68] of isosterism encompasses the aspects of the previous definitions and states that isosteres are chemical substances, atoms, or substituents that possess near equal or similar molecular shape and volume, approximately the same distribution of electrons, and which exhibit similar physicochemical properties. A few examples of isosteric atoms and substituents are provided in Figure 4.6. Many more examples are available in the literature [69-72], including metal isosteres [73]. 

---