Reaction mass relations

The general topic of this chapter is stoichiometry (stoy-key-OM-e-tree), the study of mass relations in chemistry. Whether dealing with atomic masses (Section 3.1), molar masses (Section 3.2), chemical formulas (Section 3.3), or chemical reactions (Section 3.4), you will be answering some very practical questions that ask how much or how many—." For example—... 

The approach followed in Chapter 3 to calculate mole-mass relations in reactions is readily applied to solution reactions represented by net ionic equations. 

By working parts (a) through (d) of this sample in succession, you can see how many different ways there are to ask a question about mass relations in a reaction. That should cushion the shock should you see only part (d) in an exam. 

The selection of reactor type in the traditionally continuous bulk chemicals industry has always been dominated by considering the number and type of phases present, the relative importance of transport processes (both heat and mass transfer) and reaction kinetics plus the reaction network relating to required and undesired reactions and any aspects of catalyst deactivation. The opportunity for economic... 

Yield and other mass-related metrics such as atom economy, reaction mass efficiency and mass intensity have been examined by Constable et al with regard to their significance concerning greenness and costs. The importance of using a (product) concentration term, which can be mass intensity or mass index, is additionally emphasized by Laird et al This is in compliance with Winterton, who in his twelve more green chemistry principles demands the establishment of full mass balances. 

The mass-related metrics shown in Figure 5.11 indicate that the amount of a substrate (see also byproduct formation), an auxiliary material for reaction, and of a solvent have to be reduced. The detailed view of the mass indices of the pilot scale, for example, the segments Substrates and Aux (R) and the size of segments Substrates (excess) and Aux (R) of the environmental factor E, deliver the information listed in Table 5.2 108% base and 162% auxiliary (R) are used. The measure to increase base addition for recycling purposes was successful at the expense of 193% base, much auxiliary material Aux (R) was saved in operation scale (reduction from 162% to only 13%). This leads to an overall... 

The HTE characteristics that apply for gas-phase reactions (i.e., measurement under nondiffusion-limited conditions, equal distribution of gas flows and temperature, avoidance of crosscontamination, etc.) also apply for catalytic reactions in the liquid-phase. In addition, in liquid phase reactions mass-transport phenomena of the reactants are a vital point, especially if one of the reactants is a gas. It is worth spending some time to reflect on the topic of mass transfer related to liquid-gas-phase reactions. As we discussed before, for gas-phase catalysis, a crucial point is the measurement of catalysts under conditions where mass transport is not limiting the reaction and yields true microkinetic data. As an additional factor for mass transport in liquid-gas-phase reactions, the rate of reaction gas saturation of the liquid can also determine the kinetics of the reaction [81], In order to avoid mass-transport limitations with regard to gas/liquid mass transport, the transfer rate of the gas into the liquid (saturation of the liquid with gas) must be higher than the consumption of the reactant gas by the reaction. Otherwise, it is not possible to obtain true kinetic data of the catalytic reaction, which allow a comparison of the different catalyst candidates on a microkinetic basis, as only the gas uptake of the liquid will govern the result of the experiment (see Figure 11.32a). In three-phase reactions (gas-liquid-solid), the transport of the reactants to the surface of the solid (and the transport from the resulting products from this surface) will also... 

Kushch 1, Arendacka B, Stoic S et al (2008) Breath isoprene - aspects of normal physiology related to age, gender and cholesterol profile as determined in a proton transfer reaction mass spectrometry study. Clin Chem Lab Med 46(7) 1011-1018... 

Similarity Relations for One-Dimensional, Constant-Area Channel Flow with Chemical Reactions. Similarity relations between stagnation temperature and mass fractions obtain during flow in a channel of constant cross section, provided a binary mixture approximation is used for the diffusion coefficient, the Lewis number is set equal to unity, the Prandtl number is set equal to 3/4, and a constant value is employed for the species and average isobaric specific heats. [The assumption that the species (cPii) and average (cp = 2YiCp,i) isobaric specific heats are... 

The study of enzymatic reactions in systems with substrates present at very high mass/volume ratios, often leading to suspensions rather than solutions, has also been pursued. The majority of the published work on this type of reaction was related to the synthesis of protected peptides [3-15], but the synthesis of beta-lactam antibiotics [16-19], glycosides [20, 21], glycamides [22], and esters [23-27] starting from suspended substrates has also been reported. 

Two of this year s articles discuss the fluid-mechanical aspects of systems where material transfer may occur, accompanied by chemical reaction or heat transfer. Fulford analyzes thin-film flow in terms of the flow regimes and of surface disturbances, and relates recent experimental findings to the theoretical framework. Rietema discusses segregation phenomena in heterogeneous reactions, in relation to conditions of flow and of mass transfer. 

Figures 30 and 31 refer to the excellent performance of this battery type (see Figure 31, high cell voltage of 3 V, ten times better mass-related energy content than for the lead-acid accumulator) such cells have not been commercialized up to now. This is not because of the problems to maintain the temperature—this is achieved by the waste heat—it is because the danger of crack formation and resulting catastrophic local chemical reactions that led to the fact that investigations with respect to electrotraction have been essentially abandoned.

The Hatta number Ha is a dimensionless group used to characterize the speed of reaction in relation to the diffu-sional resistance to mass transfer,... 

The reaction rate may also be expressed by the time-differential of the mass or the number of moles of reaction species. For a single reaction the reaction rate in terms of the extent of reaction is related with the reaction rate in terms of the mass m, or the number of moles nt of reaction species as shown in Eq. 1.14 ... 

The evaluation of the potential hazards associated with chemical processes and plant operational procedures is a specialised activity. In larger companies a separate group will be responsible for this activity. The work involves testing for any fire and explosion hazards associated with the chemicals and the reaction mass in which they are produced, known as the chemical reaction hazards. The process details are considered in relation to the actual chemical plant in which they are to be operated the plant operational hazards. 

Mass-related reaction rates, tm, were determined at normal pressure for the following ranges of operating conditions T = 473 to 503 K, xc6h12 = 2-6 vol%, normal pressure conditions at both membrane sides, gas hourly space velocity (GHSV) 400-1000 h-1. The composition of the effluent was measured under steady-state conditions using gas chromatography (GC). 

This polymerization type, which normally comprises noncatalyzed condensation reactions, is related to chemical reactions involving multifunctional monomers with functional groups, such as -OH, -COOH, and others [193-196], Where a multifunctional monomer is a molecule which has at least two or more reactive locations, to create intermolecular chemical bonds. The process normally comprises a sequence of condensation reactions that lead to the elimination of low mass products, for example, water [194],... 

The thermodynamic approach considers micropores as elements of the structure of the system possessing excess (free) energy, hence, micropore formation processes are described in general terms of nonequilibrium thermodynamics, if no kinetic limitations appear. The applicability of the thermodynamic approach to description of micropore formation is very large, because this one is, in most cases, the result of fast chemical reactions and related heat/mass transfer processes. The thermodynamic description does not contradict to the fractal one because of reasons which are analyzed below in Sec. II. C but the nonequilibrium thermodynamic models are, in most cases, more strict and complete than the fractal ones, and the application of the fractal approach furnishes no additional information. If no polymerization takes place (that is right for most of processes of preparation of active carbons at high temperatures by pyrolysis or oxidation of primary organic materials), traditional methods of nonequilibrium thermodynamics (especially nonequilibrium statistical thermodynamics) are applicable. 

As seen from eqs. 1 to 3, the rate of production and, consequently, the rate of catalytic reaction are related to the quantity of catalyst Q which may, for example, be expressed as the mass (mc), volume (Kc) or the surface area (Ac) of the solid catalyst. The numerical values of the corresponding specific reaction rates (rm, rv, r ) naturally differ from each other depending on the quantity to which they are related. 

Fuel Channel Mass Balance. Since the current produced by an elec-trocatalytic reaction is related to the conversion of reactive species, we can express the local mass balances in terms of local current densities, using Faraday s law. 

In addition to the rates of olefin reactions, mass transfer also plays an important role in determining the extent of propylene conversion and the product distribution from SAPO molecular sieves. Restrictions on molecular movement may be severe in the SAPO catalysts, due to pore diameters (4.3 A for SAPO-34) and structure (one-dimensional pores in SAPO-5 and SAPO-11). The deactivation of SAPO-5 and SAPO-11 catalysts may be more directly related to mass transfer than the coking of SAPO-34. Synthesis of large or highly-branched products, having low diffusivities, inside the pores of SAPO-5 or SAPO-11 essentially block internal acid... 

Two models that utilize gas-phase mass balances were proposed by Sheintuch (292). The first, a model for oxidation reactions, was related to an Eigenberger-type buffer-step model. His kinetic scheme differs, however, from the typical buffer scheme ... 

A further important aspect of the abundances of ions is their relationship to the initial structure of the sample molecule. It is often possible to deduce this structure, or elements of it, by comparison of the MS fragmentation reactions of related compounds. Examples of mass spectra are shown in Figures 1.6, 1.12 and 1.13. The reasoning used in the interpretation of a mass spectrum is based on the accumulated knowledge from the rationalisation of fragmentation mechanisms of known compounds and supported by labelling studies and the accurate mass measurement of ions. Detailed information of such mechanisms can be found in specific textbooks [14] and throughout the literature. 

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