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Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
Chemical compounds may also exist in the form of mixtures. A mixture is two or more compounds combined together without any chemical bonding taking place. Each of the compounds retains its own characteristic properties. For example, gasoline is not a pure compound. You cannot write a formula for gasoline because it is a mixture of compounds. Two types of mixtures exist: homogeneous and heterogeneous. Homogeneous means “the same kind” in Latin. In a homogeneous mixture, every part is exactly like every other part. For example, water has a molecular formula of H2O. Pure water is homogeneous; it contains no substances other than hydrogen and oxygen. Loosely translated to include mixtures, homogeneous refers to two or more compounds or elements that are uniformly dispersed in each other. A solution is another example of a homogeneous mixture. Heterogeneous means “different kinds” in Latin. In a heterogeneous mixture, different parts of the mixture have different properties. The components in a heterogeneous mixture can be separated mechanically into their component parts. Some examples of heterogeneous mixtures are gasoline, the air we breathe, blood and mayonnaise.
The second and third laws
Published in W. John Rankin, Chemical Thermodynamics, 2019
A mixture is a physical combination of two or more substances, without chemical bonding or other chemical change, in which the identities of the substances are retained. The mixing of substances, whether solid, liquid or gas, is an irreversible process and results in an increase in entropy (increased randomness). Mixing may be, and often is, constrained to occur under particular conditions. For example, the different substances may or may not be at the same temperature and pressure, and the final volume need not necessarily be the sum of the initially separate volumes. So work may be done on or by the new system during the process of mixing. However, if the final volume is the sum of the initial separate volumes and if there is no heat transfer, then no work is done. In that case, the entropy of mixing is entirely accounted for by the movement of each substance into a final volume not initially available to it.
Ignitable and Explosive Atmospheric Hazards
Published in Neil McManus, Safety and Health in Confined Spaces, 2018
Explosions involving flammable mixtures generally occur only where fuel and oxidizer have mixed intimately before ignition (Cruice 1991). As a consequence, combustion occurs very rapidly. Two types of mixtures can result: homogeneous, uniform mixtures and heterogeneous, nonuniform mixtures. The components of a homogeneous mixture are intimately and uniformly mixed. A small sample is representative of the entire mixture. Examples of substances able to form homogeneous mixtures include gases and vapors. Other types of flammable or combustible mixtures are heterogenous. Examples include mists, foams, and dusts. Gas— and vapor—air mixtures have both flammability limits (deflagration) and explosive limits. Explosive limits depend upon the initiating stimulus and the environment. They usually are slightly narrower than flammability limits. The most intense explosions of vapor—air mixtures occur near the middle of the flammable range. Explosions involving flammable vapor—air mixtures most frequently occur in confined spaces.
Exergy analysis of fusel oil as an alternative fuel additive for spark ignition engines
Published in Biofuels, 2023
Süleyman Üstün, Battal Doğan, Derviş Erol
Due to the high water content in the fusel oil, its use as a fuel in internal combustion engines has some adverse effects. For this reason, it is necessary to go through a series of steps to separate the fusel oil from the water. The basic method used to separate liquid mixtures from each other is distillation. Reducing the water content of the fusel oil will increase the combustion temperature in the cylinder, resulting in higher power output from the engine [35–37]. Chemical treatments can be used to remove some of the worthless product species in fusel oil [74]. Thus, the engine will become more efficient. Also, compression ratio changes can be made in the engine to increase efficiency in the use of fusel oil. It is predicted that exhaust emissions will be improved by reducing the water content of fusel oil [75].
An accurate water activity model for sulfuric acid solutions and its implementation on moisture sorption isotherm determination
Published in Drying Technology, 2022
Lida Zhang, Patrick M. Grace, Da-Wen Sun
In chemical engineering, a liquid mixture's component activities are crucial knowledge for the separation process design. Most of the literature models for component activity calculations are based on modeling the molecular excess Gibbs free energy and are called molecular activity models. Some well-known molecular activity models, e.g. the nonrandom two-liquid (NRTL) model[13], Wilson model[14], universal quasi-chemical (UNIQUAC) model[15] and modified NRTL (M-NRTL) models[16,17] are applicable to the correlation of vapor–liquid equilibrium (VLE) data of the H2O-H2SO4 system. Several efforts have been made to apply molecular activity models to the VLE correlation of aqueous H2SO4 at 25 °C.[18–21] With the use of an accurate thermodynamic calculation described by Wilson,[1] the predicted VLE data at 25 °C can be converted to VLE data at different temperatures. However, as far as we know, only three works have modeled the VLE of the H2O-H2SO4 system covering the whole concentration range and the temperature range of 0 ∼ 100 °C.[22–24] All their modeling details are summarized in Table 1.
A regularizing Kohn–Vogelius formulation for the model-free adsorption isotherm estimation problem in chromatography
Published in Applicable Analysis, 2018
G. Lin, Y. Zhang, X. Cheng, M. Gulliksson, P. Forssén, T. Fornstedt
The separation and purification of the components in a mixture are important processes in many industries, including the fine chemical, pharmaceutical, biomedical, and food industries. Chromatography is a common method used in separation processes to isolate one or several components from a mixture [1]. The mechanism of chromatography is based on the fact that different solutes in the sample interact differently with the stationary phase: some are strongly adsorbed whereas others are barely retained. The outcome of a chromatographic separation is strongly dependent on the adsorption isotherms of the solutes, since they dictate the separation factors and saturation capacities, i.e. how much solute can be adsorbed. Therefore, how to determine adsorption isotherms is an issue of significant importance in chromatography.