Substance defined

Enthalpy. Enthalpy is the thermodynamic property of a substance defined as the sum of its internal energy plus the quantity Pv//, where P = pressure of the substance, v = its specific volume, and J = the mechanical equivalent of heat. Enthalpy is also known as total heat and heat content. 

The change in Gibbs s free energy (defined, as stated, for a system at constant pressure and temperature) when a moles of A and b moles of B are converted into c moles of C and d moles of D is AG = cpc +dpD - apA - bpB, where p represent chemical potentials , i.e. free energy per mole of the substances, defined in terms of concentration of a component X as... 

Saltpeter plus charcoal yields an alkali salt which hath a taste like that of the Salt of Tartar [potassium carbonate], and they differ but little in virtue.He does not say they are identical, though they would both be impure potassium carbonate. There simply did not exist at this time a clear conception of the idea of chemical substance, defined by material composition. The chief means of identifying an artificially prepared body was by its method of preparation. The inevitable presence of impurities made precise identification by explicit properties uncertain in any case, and here Lemery exhibits proper caution in indicating only the similarity rather than the identity of salt of tartar and the product of charcoal in molten saltpeter. 

Flavouring substances are chemically defined substances with flavouring properties. There are three different categories of flavouring substances defined in the definitions of the lOFI Code of Practice and EU Flavour Directive 88/388/ EEC [1,2] ... 

The European system for regulating synthetic chemicals, described in Chapter 5, is predominantly risk-based . This means that restrictions on the manufacture or use of chemicals must be justified by reference to evidence that there is a risk of the chemical causing a specified type of harm. REACH (Registration, Evaluation, Authorization and restriction of Chemicals) does not define the term risk , but the directive on risk assessment of new substances defined it as the incidence and severity of the adverse effects likely to occur [...] due to actual or predicted exposure to a substance (Article 2 of Directive 93/67/EEC). In the first part of this chapter I look at how risks from chemicals are assessed. What does chemicals risk assessment in practice aim to achieve Can it provide the reliable evidence needed for agreement by all parties on whether or not a chemical poses a risk My answer to this second question is no there are multiple uncertainties in chemicals risk assessment which lead to protracted debates as to whether a chemical poses a risk or not. 

To understand the significance of material properties, one only has to think of density, which is also a material property. The density of a substance defines how much volume, let s say, of water, that the substance will displace on immersion. Instead of measuring the volume of water each time one drops this substance in any container of water, one measures its density and calculates how much water it will displace on immersion. Clearly, the material property concept leads to predictive abilities. It is now known that the relative ordering of the molecules in a simple bodymatter defines its density and that by altering the ordering of the molecules, one... 

Legislation on packaging and labelling of dangerous substances defines hazardous chemicals under the following categories ... 

Rh Dimensionless retardation factor of the humic substances, defined in Eq. (50)... 

The heat content of a specific amount of substance defined as E= PV. 

Standard state a reference state for a specific substance defined according to a set of conventional definitions. (9.6) Standard temperature and pressure (STP) the condition 0°C and 1 atm of pressure. (5.4)... 

For drug substances defined as hydrates or solvates, an assay value consistent with the anhydrous, solvent-free basis can be calculated where the amount of water or solvents subtracted in the denominator is the difference between the measured and theoretical amounts. 

Monitoring surface water, ground water, seawater, effluents and drinking water for toxic compounds is traditionally carried out by discrete (spot) sampling that is followed by chemical analysis in the laboratory. This provides qualitative and quantitative information on specific analytes, in Europe often focused on the priority substances defined by the EC Water Framework Directive, WFD (European Commission, 2000). Although... 

The crucial event in Lavoisier s career was his realization that air (which nearly everyone believed to be a simple substance defined by its physical, rather than by any chemical, properties) must play a part in chemical transformations - most dramatically those observed in ordinary combustion, the roasting (calcining) of metals, and the reduction of ores or cakes . ... 

For each document type, a document contents model determines which entities from the partial models ontologies can be contained in a corresponding document instance. For instance, the PFD document can contain arbitrary process steps defined in the partial model process as well as substances defined in the partial model chemical process material. Fine-grained interdocument relationships that are not already included in the ontologies are added. Furthermore, the document structure can be refined, indicating the order or the type of structural entities (such as heading, text block, or table) that have to be contained in the document (cf. Subsect. 2.3.4). 

Rule scripts operate on substances defined in a data file in either SMILES (simplified molecular input line entry specification) or CMP (compound) format. The conventional SMILES notation as developed by Weininger [28] provides a basic description of molecules in terms of two-dimensional chemical graphs. The CMP file format developed with the OASIS system [29] provides separate logical records for information about connectivity, three-dimensional structure, electronic structure from quantum-chemical molecular-orbital computations, as well as physicochemical and experimental toxicological data. 

MAK-value Maximum workplace concentration, product-specific value of chemical substances defining the harmful contamination of the air at the workplace due to these substances (dimension ppm = parts per million = mg/kg). Information on MAK-values are given in the safety data sheets of the respective substances. 

Specific rotation [u] - For an optically active substance, defined by [ ] = a/y/, where a is the angle through which plane polarized light is rotated by a solution of mass concentration y and path length 1. Here 0 is the Celsius temperature and X the wavelength of the light at which the measurement is carried out. Also called specific optical rotatory power. [2]... 

The lipids are a group of substances defined in terms of their solubility characteristics. They are water-insoluble substances that can be extracted from cells by organic solvents such as benzene. The lipids found in the human body can be divided into four classes according to their molecular structure fats, phospholipids, waxes, and steroids. 

In the case of a class-2 substance—defined under the EPA s TSCA regulations as a substance whose composition cannot be represented by a definite chemical structure diagram—the substance may be identified on the TSCA Inventory in a less precise manner, e.g., Cg g alkenes. Persons using the TSCA Inventory are cautioned that such a category is not intended to encompass class-1 substances, defined under the EPA s TSCA regulations as substances that can be more precisely described. For example, 1-hexene, if manufactured as such, is considered a different substance than Cg.g alkenes, ... 

Active oxidising compounds can also be made in a small reactor by nfixing an oxidising compound with another material to produce a new compound, which is then immediately fed to the paper machine (so-called in situ generation). One example of this is ammonium bromide reacted with hypochlorite to form a substance defined as bromo-activated chloramines. A further example is the corresponding process starting with ammonium sulphate and hypochlorite as the two reactants. 

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