Exothermic definition

The term lime also has a broad coimotation and frequently is used in referring to limestone. According to precise definition, lime can only be a burned form quicklime, hydrated lime, or hydraiflic lime. These products are oxides or hydroxides of calcium and magnesium, except hydraiflic types in which the CaO and MgO are chemically combined with impurities. The oxide is converted to a hydroxide by slaking, an exothermic reaction in which the water combines chemically with the lime. These reversible reactions for both high calcium and dolomitic types are Quicklime... 

Thermoanalytical methods (tga, dta) often enable definite identification of the type of asbestos fibers (Fig. 7). For example, the strong exotherm observed with chrysotile at 830°C can be used as a routine indicator for determining the chrysotile content of talc (4,10). Thermal methods are also usefiil for determining certain mineral contaminants of asbestos fibers, for example bmcite and calcite in chrysotile. 

Reducing agents present similar problems. They react with a broad spectrum of chemical classes, and the reactions can be exothermic and violent. Reducing agents are, by definition, highly oxidizable and may react with air or moisture in the air. Common reducing agents include ... 

A typical exothermic profile for HEMA polymerization is shown in Figure 1 which also exemplified the definitions of peak time and stall time. 

NFPA now normally refers to autoignition as the Hot Flame Ignition Temperature, as a more precise definition. Subsequently the following two additional terms are being adopted by NFPA to further refine the ignition properties of materials. The lowest temperatures at which cool flame ignitions are observed are named the Cool Flame Reaction Threshold (CFT). The lowest flame temperatures at which an exothermic gas phase reaction is noticed are named the Preflame Reaction Threshold (RTT). 

We have already noted that the process was exothermic (the value is negative) and should be reported as -28.50606 kJ (unrounded). The sign comes from convention (the definition of exothermic) and not from the calculation. 

The coupling of SR with POX is termed autothermal reforming (ATR). The exact definition varies. Some define ATR as an SR reaction and a POX reaction that take place over microscopic distances at the same catalytic site thus avoiding complex heat exchanging (16). Others have the less restrictive definition that ATR occurs when there is no wall between a combined SR reaction and catalytic POX reaction. ATR is carried out in the presence of a catalyst that controls the reaction pathways and thereby determines the relative extents of the POX and SR reactions. The SR reaction absorbs part of the heat generated by the POX process reaction, limiting the maximum temperature in the reactor. The net result is a slightly exothermic process. 

The arguments advanced in Sect. 3.2.3 apply equally well to a continuous stirred tank reactor. With a reversible exothermic reaction and a fixed mean residence time, t, there is an optimum temperature for operation of a continuous stirred tank reactor. Since the conditions in an ideal stirred tank are, by definition, uniform, there is no opportunity to employ a temperature gradient, as with the plug-flow reactor, to achieve an even better performance. 

Exothermic Reaction. A reaction in which heat is liberated. It usually proceeds rapidly sometimes explosively. In an endothermic reaction a chemical change proceeds slowly with absorption of a definite number of calories Ref Hackh s (1944), 328-R (Exothermic) 305 R (Endothermic)... 

Erdey-Gruz, 1048, 1306 1474 Erschler, 1133, 1134, 1425 Ethylene oxidation, anodic, 1052 1258 Exchange current density, 1049, 1066 correction of, 1069 definition, 1053 electrocatalysis and, 1278 impedance and, 1136 interfacial reaction, 1047 and partly polarizable interface, 1056 Excited states, lifetime, 1478 Exothermic reaction, 1041 Ex situ techniques, 785, 788, 1146... 

Phase diagrams from freezing point depressions show true compound formations for simpler amides—e.g., water-N-methylacetamide forms a compound at a mole ratio of 2 to 1, water-N,N-dimethylacetamide at 3 to 2 and 3 to 1, and water-N-methylpyrrolidone at 2 to 1. The heats of mixing and heat capacities at 25°C. of a number of water-amide systems were determined. All mixing curves were exothermic and possess maxima at definite mole ratios, while the heat capacities for the most part show distinct curvature changes at the characteristic mole ratios. Both experimental results point to the stability of the particular complexes even at room temperature. This is further supported by absolute viscosity studies over the whole concentration range where large maxima occur at these same mole ratios for disubsti-tuted amides and N-substituted pyrrolidones. 

It is easy to see some of the factors affecting the equilibrium composition. From the definition in Eq. 9.42, large values of Kp dictate that the products of the reaction are favored over the reactants that is, thermodynamics pushes the forward reaction toward completion. From Eq. 9.44, a reaction that is very exothermic, AH° << 0, favors product formation that is, Kp will be very large. 

Note that the definition of electron affinity does not follow the usual thermodynamic convention in ihat a positive electron affinity is exothermic. See Chapter 2. 

This definition excludes those exothermic reactions which shown and increase in rate with time (like explosions caused by the rapidly rising temperature. 

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