Physical properties, pure substances

Elements and compounds constitute the world of pure substances. An element is a substance that cannot be decomposed by any chemical reaction into simpler substances. Elements are composed of only one type of atom and all atoms of a given type have the same properties. Pure substances cannot be separated into other kinds of matter by any physical process. We are familiar with many pure substances water, iron, mercury, iodine, helium, rust, diamond, table salt, sugar, gypsum, and so forth. Among the pure substances listed above, iron, mercury, iodine, diamond (pure carbon), and helium are elements. We are also familiar with mixtures of pure substances. These include the air that we breathe, milk, molasses, beer, blood, coffee, concrete, egg whites, ice cream, dirt, steel, and so on. 

As we previously learned, mixtures are not pure substances. In order to obtain one of the components in a mixture, we need to separate them. The separation of mixtures can only be possible when we use the physical properties of substances. 

Density is a characteristic physical property of substances (see Table 1.4) that depends on temperature. Density is an example of an intensive property, one that is independent of the amount of the substance. The density of aluminum, for example, is the same whether you have a gram or a kilogram. Intensive properties are often used to identify substances because these properties depend only on the type of substance, not on the amount of it. For example, from Table 1.4 on the next page you can see that pure gold has a density of 19.3 g/cm. One way to determine whether a substance is pure gold is to determine its density and compare it to 19.3 g/cm. Mass, in contrast, is an extensive property, one that depends on the amount of the substance. If you know only the mass of a sample of gold, that information alone will not allow you to identify it as gold. 

The thermodynamic and physical properties of pure steam are well estabUshed over the range of pressures and temperatures used. The chemical properties of steam and of substances ia steam, their molecular stmctures, and iateractions with the soHd surfaces of containments need to be more fliUy explored. 

Physical Properties. The physical properties of the provitamins and vitamins D2 and are Hsted ia Table 6. The values are Hsted for the pure substances. The D vitamins are fat-soluble and, as such, are hydrophobic. 

AU substances are listed in alphabetical order in Table 2-6(3. Compiled from Daubert, T E., R. R Danner, H. M. Sibiil, and C. C. Stebbins, DIPPR Data Compilation of Pure Compound Properties, Project 801 Sponsor Release, July, 1993, Design Institute for Physical Property Data, AlChE, New York, NY and from Thermodynamics Research Center, Selected Values of Properties of Hydrocarbons and Related Compounds, Thermodynamics Research Center Hydrocarbon Project, Texas A M University, College Station, Texas (extant 1994). 

The material in this section is divided into three parts. The first subsection deals with the general characteristics of chemical substances. The second subsection is concerned with the chemistry of petroleum it contains a brief review of the nature, composition, and chemical constituents of crude oil and natural gases. The final subsection touches upon selected topics in physical chemistry, including ideal gas behavior, the phase rule and its applications, physical properties of pure substances, ideal solution behavior in binary and multicomponent systems, standard heats of reaction, and combustion of fuels. Examples are provided to illustrate fundamental ideas and principles. Nevertheless, the reader is urged to refer to the recommended bibliography [47-52] or other standard textbooks to obtain a clearer understanding of the subject material. Topics not covered here owing to limitations of space may be readily found in appropriate technical literature. 

Pure substance, phase behavior of, 24 663 Pure supercritical fluids, physical properties of, 24 4... 

Molecules which exhibit optical activity are molecules which have a handedness in their structure. They are chiral . Chemists often have reasons to obtain chemical pure aliquots of particular molecules. Since the chirality of molecules can influence biological effect in pharmaceuticals, the chiral purity of a drug substance can pose a challenge both in terms of obtaining the molecules and in assaying the chiral purity by instrumental methods. While diastereomers can have different physical properties including solubility, enantiomers have the same physical properties and the same chemical composition. How then to separate optically active molecules ... 

Unsurprisingly, a SCF has many physical properties that are intermediate between those of a liquid and a gas. Table 6.2 shows a comparison of typical values for physical properties of a pure substance in different phases. 

The physical-chemical properties of a supercritical fluid are between those of liquids and gases supercritical fluids (SCFs) indicate the fluid state of a compound in pure substance or as the main component above its critical pressure (pc) and its critical temperature (Tc), but below the pressure for phase transition to the solid state, and in terms of SCF processing, a density close to or higher than its critical density. 

A phase is defined as a state of matter that is uniform throughout in terms of its chemical composition and physical state in other words, a phase may be considered a pure substance or a mixture of pure substances wherein intensive properties do not vary with position. Accordingly, a gaseous mixture is a single phase, and a mixture of completely miscible liquids yields a single hquid phase in contrast, a mixture of several solids remains as a system with multiple solid phases. A phase rule therefore states that, if a limited number of macroscopic properties is known, it is possible to predict additional properties. 

Results of the Vickers hardness of 15 inorganic and organic salts will be presented. The hardness-force dependency, and the effects of direction dependency were examined. The measured values of the Vickers hardnesses were taken for an attempt to prove a model to calculate the hardness. This model describes the hardness purely by physical properties of the substances. The use of such a model may be an approach for the description of the abrasion resistance of salts. Data describing the abrasion resistance could help in the understanding and interpretation of secondary nucleation phenomena. 

Refractive index or index of refraction is the ratio of wavelength or phase velocity of an electromagnetic wave in a vacuum to that in the substance. It measures the amount of refraction a ray of light undergoes as it passes through a refraction interface. Refractive index is a useful physical property to identify a pure compound. 

To design a supercritical fluid extraction process for the separation of bioactive substances from natural products, a quantitative knowledge of phase equilibria between target biosolutes and solvent is necessary. The solubility of bioactive coumarin and its various derivatives (i.e., hydroxy-, methyl-, and methoxy-derivatives) in SCCO2 were measured at 308.15-328.15 K and 10-30 MPa. Also, the pure physical properties such as normal boiling point, critical constants, acentric factor, molar volume, and standard vapor pressure for coumarin and its derivatives were estimated. By this estimated information, the measured solubilities were quantitatively correlated by an approximate lattice equation of state (Yoo et al., 1997). 

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