Exothermicity factor

The reaction is exothermic. For (3 = 1.2 the exothermicity factor, and 7 the dimensionless activities factor, find the range of a, the dimensionless preexponential factor, that gives multiplicity of steady states using a suitable MATLAB program with Kc = 0, the dimensionless heat transfer coefficient of the cooling jacket. Choose a value of a in the multiplicity region and obtain the multiple steady-state dimensionless temperatures and concentrations. 

FIGURE 5.56 Effect of exothermicity factor on the effectiveness factor of a bimolecuiar reaction 0 =. ... 

The equilibrium constant of the reaction is independent of temperature and is equal to 16.5. The dimensionless activation energy for the forward reaction is equal to 18, the net dimensionless exothermicity factor is equal to 0.7, and the external mass and heat transfer resistances are negligible. 

Reactions in porous catalyst pellets are Invariably accompanied by thermal effects associated with the heat of reaction. Particularly In the case of exothermic reactions these may have a marked influence on the solutions, and hence on the effectiveness factor, leading to effectiveness factors greater than unity and, In certain circumstances, multiple steady state solutions with given boundary conditions [78]. These phenomena have attracted a great deal of interest and attention in recent years, and an excellent account of our present state of knowledge has been given by Arls [45]. 

Many programs allow the user to input a weighting factor (i.e., to give a structure that is 70% of the way from reactants to products). This allows the application of the Hammond postulate that the transition structure will look more like the reactants for an exothermic reaction and more like the products for an endothermic reaction. 

The derivatives are hydroxyethyl and hydroxypropyl cellulose. AH four derivatives find numerous appHcations and there are other reactants that can be added to ceUulose, including the mixed addition of reactants lea ding to adducts of commercial significance. In the commercial production of mixed ethers there are economic factors to consider that include the efficiency of adduct additions (ca 40%), waste product disposal, and the method of product recovery and drying on a commercial scale. The products produced by equation 2 require heat and produce NaCl, a corrosive by-product, with each mole of adduct added. These products are produced by a paste process and require corrosion-resistant production units. The oxirane additions (eq. 3) are exothermic, and with the explosive nature of the oxiranes, require a dispersion diluent in their synthesis (see Cellulose ethers). 

Solution Polymerization. Plant scale polymerizations ia water are conducted either adiabaticaHy or isotherm ally. Molecular weight control, exotherm control, and reduction of residual monomer are factors which limit the types of initiators employed. Commercially available high molecular weight solution polyacrylamides are usually manufactured and sold at about 5% soHds so that the viscosities permit the final product to be pumped easily. 

Acrylate and methacrylate polymerizations are accompanied by the Hberation of a considerable amount of heat and a substantial decrease in volume. Both of these factors strongly influence most manufacturing processes. Excess heat must be dissipated to avoid uncontrolled exothermic polymerizations. In general, the percentage of shrinkage decreases as the size of the alcohol substituent increases on a molar basis, the shrinkage is relatively constant (77). 

No external heat source is required. In all types of steelmaking that employ pig iron, which melts at temperatures well below low carbon steel, the heat balance between exothermic oxidation of elements, such as C, Si, and Mn, and the cooling provided by scrap or sometimes other endothermic coolants, such as iron ore, are critical issues. The numerical factors are well understood and are routinely contained in computer programs used by operators. If the balance is such that the temperature after blowing is too high, refractory consumption is increased significantly. 

An equimolar mixture of carbon monoxide and chlorine reacts at 500 K under a slight positive pressure. The reaction is extremely exothermic (Ai/gQQp. = —109.7 kJ or —26.22 kcal), and heat removal is the limiting factor in reactor design. Phosgene (qv) is often produced on-site for use in the manufacture of toluene diisocyanate (see Amines, aromatic-diaminotoluenes Isocyanates, organic). 

Decompositions may be exothermic or endothermic. Solids that decompose without melting upon heating are mostly such that can give rise to gaseous products. When a gas is made, the rate can be affected by the diffusional resistance of the product zone. Particle size is a factor. Aging of a solid can result in crystallization of the surface that has been found to affect the rate of reaction. Annealing reduces strains and slows any decomposition rates. The decompositions of some fine powders follow a first-order law. In other cases, the decomposed fraction x is in accordance with the Avrami-Erofeyev equation (cited by Galwey, Chemistry of Solids, Chapman Hall, 1967)... 

Treatment of thermal conductivity inside the catalyst can be done similarly to that for pore diffusion. The major difference is that while diffusion can occur in the pore volume only, heat can be conducted in both the fluid and solid phases. For strongly exothermic reactions and catalysts with poor heat conductivity, the internal overheating of the catalyst is a possibility. This can result in an effectiveness factor larger than unity. 

A critical factor is the boiling temperature of the blowing agent and its relationship to the temperature of the walls of the mould and of the reacting mixture. There should be sufficient exotherm to vaporise the blowing agent in the centre of the reacting material but the mould walls should be sufficiently cool to... 

Safety in Chemical Reaction Engineering 911 Other factors that are responsible for exothermic incidents are ... 

The chemical reaction rate is generally a function of a reactant concentration and temperature. In the case of an exothermic reaction, unless the heat of reaction is removed, an increase in temperature may result in a runaway reaction. For most homogeneous reaction, the rate is increased by a factor of 2 or 3 for every 10°C rise in temperature. This is represented by... 

The reaction is significantly exothermic with a heat of reaction of about 40 kcalmol . This energy will produce a sufficiently high temperature to melt the product and will allow the influence of thermochemical factors to be investigated. The temperature required to initiate the Ni-Al reaction at atmospheric pressure is about 660 °C. This reaction temperature threshold will be encountered in the shock processing, but it should be recognized that the conventional synthesis process is preceded by melting of the aluminum. At the pressure of the shock compression, the melt temperature of the aluminum will be approximately doubled to a value above the mean-bulk tempera-... 

It is more common to find that AH° and AS° have the same sign (Table 17.2, III and IV). When this happens, the enthalpy and entropy factors oppose each other. AG° changes sign as temperature increases, and the direction of spontaneity reverses. At low temperatures, AH° predominates, and the exothermic reaction, which may be either the forward or the reverse reaction, occurs. As the temperature rises, the quantity TAS° increases in magnitude and eventually exceeds AH°. At high temperatures, the reaction that leads to an increase in entropy occurs. In most cases, 25°C is a low temperature, at least at a pressure of 1 atm. This explains why exothermic reactions are usually spontaneous at room temperature and atmospheric pressure. 

In chlorinations either a substitution or an addition process can occur with the ultimate reaction pathway(s) determined by a combination of factors, which include the reaction conditions, the positions and natures of any substituents present, and the catalyst used. Uncatalyzed chlorination of benzothiadiazole is an exothermic reaction that gives rise to a mixture of isomeric tetrachloro addition products. These are converted in basic medium into 4,7-dichloro-2,1,3-benzothiadiazole (70RCR923). When an iron(III) catalyst is present 4- and 7-chloro substitution becomes the dominant process. Chlorination of a number of 4-substituted 2,1,3-benzothiadiazoles (43) using an oxidative process gave a combination of chlorinated and oxidized products. The 4-hydroxy, 4-amino-, 4-methyl-amino, and 4-acetoxy derivatives of 43 all formed the chloroquinones (44) (40-61% yields). With the 4-aIkoxy substrates both 44 and some 5,7-dichlorinated product were obtained (88CHE96). 

The thermal behavior of Li, Ni02 in relation to safety is another key factor when in considering materials for lithium-ion batteries. LiNi02 is stable even when it is heated with an organic electrolyte. However, partially or fully oxidized LiNi02 is quite active toward organic electrolyte oxidation and this reaction is exothermic. 

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