Stoichiometric proportions

The breaking up of azeotropic mixtures. The behaviour of constant boiling point mixtures simulates that of a pure compound, because the composition of the liquid phase is identical with that of the vapour phase. The composition, however, depends upon the pressure at which the distillation is conducted and also rarely corresponds to stoichiometric proportions. The methods adopted in practice will of necessity depend upon the nature of the components of the binary azeotropic mixture, and include —... 

Stoichiometric Proportions. The stoichiometric proportions of the constituents in a formula may be denoted by Greek numerical prefixes mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- (Latin), deca-, undeca- (Latin), dodeca-,. . . , icosa- (20), henicosa- (21),. . . , tri-conta-(30), tetraconta-(40),. . . , hecta-(100), and so on, preceding without a hyphen the names of the elements to which they refer. The prefix mono can usually be omitted occasionally hemi-(1/2) and sesqui- (%) are used. No elisions are made when using numerical prefixes except in the case of icosa- when the letter i is elided in docosa- and tricosa-. Beyond 10, prefixes may be replaced by Arabic numerals. 

Multiplicative Prefixes. The multiplicative prefixes bis, tris, etc., are used with certain anions for indicating stoichiometric proportions when di, tri, etc., have been preempted to designate condensed anions for example, A1K(S04)2 I2H2O, aluminum potassium bis(sulfate) 12-water (recall that disulfate refers to the anion S20jfi. 

Of course, in reactions (5.A) and (5.B) the hydrocarbon sequences R and R can be the same or different, contain any number of carbon atoms, be linear or cyclic, and so on. Likewise, the general reactions (5.C) and (5.E) certainly involve hydrocarbon sequences between the reactive groups A and B. The notation involved in these latter reactions is particularly convenient, however, and we shall use it extensively in this chapter. It will become clear as we proceed that the stoichiometric proportions of reactive groups-A and B in the above notation—play an important role in determining the characteristics of the polymeric product. Accordingly, we shall confine our discussions for the present to reactions of the type given by (5.E), since equimolar proportions of A and B are assured by the structure of this monomer. 

The product of this reaction can be removed as an azeotrope (84.1% amide, 15.9% acetic acid) which boils at 170.8—170.9°C. Acid present in the azeotrope can be removed by the addition of soHd caustic soda [1310-73-2] followed by distillation (2). The reaction can also take place in a solution having a DMAC-acetic acid ratio higher than the azeotropic composition, so that an azeotrope does not form. For this purpose, dimethylamine is added in excess of the stoichiometric proportion (3). If a substantial excess of dimethylamine reacts with acetic acid under conditions of elevated temperature and pressure, a reduced amount of azeotrope is formed. Optimum temperatures are between 250—325°C, and pressures in excess of 6200 kPa (900 psi) are requited (4). DMAC can also be made by the reaction of acetic anhydride [108-24-7] and dimethylamine ... 

Dimethylamine is added somewhat in excess of the stoichiometric proportion in this synthesis. Another method employs the reaction of methyl acetate [79-20-9] and dimethylamine ... 

Pure ammonium nitrate decomposes in a complex manner in a series of progressive reactions having different thermochemical effects (Table 17). Oxygen is Hberated from combination with combustibles only at temperatures above 300°C. When a combustible material such as fuel oil is present in stoichiometric proportions (ca 5.6%) the energy evolved increases almost threefold... 

An early method of preparation of KAIF (42) involved combining aqueous solutions of HF, A1F., and KHF2 in stoichiometric proportions and evaporating the suspension to a dry mixture. The product was subsequently melted and recrystaUized. Some of the other conventional technical methods... 

Because this reaction is highly exothermic, the equiUbrium flame temperature for the adiabatic reaction with stoichiometric proportions of hydrogen and chlorine can reach temperatures up to 2490°C where the equiUbrium mixture contains 4.2% free chlorine by volume. This free hydrogen and chlorine is completely converted by rapidly cooling the reaction mixture to 200°C. Thus, by properly controlling the feed gas mixture, a burner gas containing over 99% HCl can be produced. The gas formed in the combustion chamber then flows through an absorber/cooler to produce 30—32% acid. The HCl produced by this process is known as burner acid. 

FerroteUurium or iron teUuride [12125-63-2] FeTe, which usually has a Te content near the theoretical 69.5%, is made by the exothermic melting iron and tellurium powders in stoichiometric proportions. 

Calcareous minerals and evaporite minerals (haUdes, gypsum) are very soluble and dissolve rapidly and, in general, congmendy, ie, yielding upon dissolution the same stoichiometric proportions in the solution as the proportions in the dissolving mineral and without forming new soHd phases (Fig. 

Chlorination with Other Reagents. Chlorotoluenes can also be obtained in good yields by the reaction of toluene with stoichiometric proportions of certain Lewis acid chlorides such as inon(III) chloride, as the chlorinating agent (51). Generally, the product mixture contains /)-chlorotoluene as the principal component. Several modifications have been proposed to improve product yields (52,53). 

Stoichiometric proportions. Constituent proportions of the reaetants are sueh that there are exaetly enough oxidizer moleeules to bring about a eomplete reaetion to stable moleeular forms in the produets. 

On the basis of an extended experimental program described in Section 4.1.3, Harris and Wickens (1989) concluded that overpressure effects produced by vapor cloud explosions are largely determined by the combustion which develops only in the congested/obstructed areas in the cloud. For natural gas, these conclusions were used to develop an improved TNT-equivalency method for the prediction of vapor cloud explosion blast. This approach is no longer based on the entire mass of flammable material released, but on the mass of material that can be contained in stoichiometric proportions in any severely congested region of the cloud. 

The chief advantages in NCN blasting agent use are related to economy, efficiency and safety. In certain applications, an overall cost saving of up to 75% over conventional NG expls has been reported. Where used.under well-controlled conditions, it is reported to perform as well as or better than Dynamites, and, by virtue of its greater gas production, may even give better fragmentation. It is safer to handle and use because its hazard sensitivity is low, and misfires are easily and safely resolved. One of its important virtues is that it is not classified as an explosive but when mixed in the correct stoichiometric proportions under preferred physical con-... 

Stronger reducing agents than Cu1 can be used for reactions that are related to the classical Meerwein reaction. Tim salts not only catalyze the formation of aryl radicals from diazonium ions but, as shown by Citterio and Vismara (1980) and Cit-terio et al. (1982 a), in stoichiometric proportions they also reduce the primary aryl-ethane radical to the arylethyl anion, which is finally protonated by the solvent SH (Scheme 10-61). This method is the subject of a contribution to Organic Syntheses (Citterio, 1990), in which 4-(4 -chlorophenyl)buten-2-one is obtained in 65-75% yield from 4-chlorobenzenediazonium chloride and but-3-en-2-one. 

Examples 1,1, and 2 in H2 + Br2 - 2 HBr. stoichiometric point The stage in a titration when exactly the right volume of solution needed to complete the reaction has been added, stoichiometric proportions Reactants in the same proportions as their coefficients in the chemical equation. Example equal amounts of H2 and Br2 in the formation of HBr. 

By contrast with tertiary amines used in catalytic quantities, primary and secondary amines or acid anhydrides may be used to bring about the cure of epoxy resins by reaction in stoichiometric proportions. A typical amine curing agent used at this level is diaminodiphenylmethane (DDM), which reacts with an individual epoxy-group in the way shown in Reaction 4.17. 

Instantaneous images obtained in a turbulent premixed V-shaped flame configuration, methane and air in stoichiometric proportions. (Reproduced from Kobayashi, H., Tamura, T., Maruta, K., Niioka, T, and Williams, F. A., Proc. Combust. Inst., 26,389,1996. With permission. Figure 2, p. 291, copyright Combustion Institute.)... 

In contrast in presence of calcium or copper the phase separation took place for low values of the added salts and almost in stoichiometric proportion with the COO" concentration. As shown in Figure 1 the addition of monovalent... 

The depression of the molecular weight brought about by nonequivalence of reactants, by monofunctional ingredients, or by unbalance in the stoichiometric proportions may be expressed quantitatively as follows. Suppose that a small amount of a reactant designated by B—I—B is added either to a pure A-------B monomer or to an... 

In industrial reactions the components are seldom fed to the reactor in exact stoichiometric proportions. A reagent may be supplied in excess to promote the desired reaction to maximise the use of an expensive reagent or to ensure complete reaction of a reagent, as in combustion. 

If one has a feed stream containing these gases in stoichiometric proportions (H2/CO = 2) at 200 atm and 275 °C, determine the effluent composition from the reactor ... 

Systems composed of stoichiometric proportions of reactants also have rate expressions that will often degenerate to the above form. 

Studies of the influence of total pressure on the initial reaction rate for pure reactants present in stoichiometric proportions provide a means of discriminating between various classes of Hoqgen-Watson models. Isolation of a class of probable models by means of plots of initial reaction rate versus total pressure, feed composition, and temperature constitutes the first step n developing a Hougen-Watson rate model. Hougen (14) has considered the influence of total pressure for unimolecular and bimolecular surface reactions the analysis that follows is adopted from his monograph. 

Mixtures of stoichiometric proportions (zero oxygen balance) are a high deflagration hazard and show remarkable pressure increase effects on ignition [1], as well as lowest ignition temperatures by ARC [2],... 

A second general approach is to use an alkali metal in conjunction with an electron carrier such as naphthalene. The electron carrier is normally used in less than stoichiometric proportions, generally 5 to 10 mole percent based on the metal salt being reduced. This procedure allows reductions to be carried out at ambient temperatures or lower in contrast to the previous approach which requires refluxing. A convenient reducing metal is lithium. 

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