Reactions, highly exothermic, flame

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. 

Adiabatic Reaction Temperature (T ). The concept of adiabatic or theoretical reaction temperature (T j) plays an important role in the design of chemical reactors, gas furnaces, and other process equipment to handle highly exothermic reactions such as combustion. T is defined as the final temperature attained by the reaction mixture at the completion of a chemical reaction carried out under adiabatic conditions in a closed system at constant pressure. Theoretically, this is the maximum temperature achieved by the products when stoichiometric quantities of reactants are completely converted into products in an adiabatic reactor. In general, T is a function of the initial temperature (T) of the reactants and their relative amounts as well as the presence of any nonreactive (inert) materials. T is also dependent on the extent of completion of the reaction. In actual experiments, it is very unlikely that the theoretical maximum values of T can be realized, but the calculated results do provide an idealized basis for comparison of the thermal effects resulting from exothermic reactions. Lower feed temperatures (T), presence of inerts and excess reactants, and incomplete conversion tend to reduce the value of T. The term theoretical or adiabatic flame temperature (T,, ) is preferred over T in dealing exclusively with the combustion of fuels. 

The fluidized-bed process for this reaction has several advantages over a fixed-bed process. First, the process is highly exothermic, and the selectivity to C3H3N is temperature dependent. The improved temperature control of the fluidized-bed operation enhances the selectivity to acrylonitrile, and substantially extends the life of the catalyst, which readily sinters at temperatures in excess of 800 K. Furthermore, since both the reactants and products are flammable in air, the use of a fluidized bed enables the moving particles to act to quench flames, preventing combustion and ensuring safe operation. 

Magnesium ribbon burns in air in a highly exothermic combustion reaction. (See equation (1).) A very bright flame accompanies the production of magnesium oxide, as shown in the photograph below. It is impractical and dangerous to use a coffee-cup calorimeter to determine the enthalpy change for this reaction. 

The combustion of gasoline is a fast and highly exothermic reaction. Gasoline is stored in a car s fuel tank, where it is exposed to oxygen in the air. Why does gasoline in a fuel tank not burst into flames spontaneously ... 

The third chemical equation, involving nitric oxide, represents a termolecular reaction. Therefore, the overall order of the reaction is expected to exceed that of the second-order reaction generally assumed in the pre-mixed gas burning model. The high exothermicity accompanying the reduction of NO to N2 is responsible for the appearance of the luminous flame in the combustion of a double-base propellant, and hence the flame disappears when insufScient heat is produced in this way, i. e., during fizz burning. 

In the dark zone, the temperature increases relatively slowly and so for the most part the temperature gradient is much less steep than that in the fizz zone. However, the temperature increases rapidly at about 50 pm from where the flame reaction starts to produce the luminous flame zone. The gas flow velocity increases with increasing distance due to the increase in temperature. The mole fractions of NO, CO, and Hj decrease and those of N2, CO2, and H2O increase with increasing distance in the dark zone. The results imply that the overall reaction in the dark zone is highly exothermic and that the order of reaction is higher than second order because of the reduction reaction involving NO. The derivative of temperature with respect to time t in the dark zone is expressed empirically by the formulal =l... 

This reaction is highly exothermic without yielding gaseous products, i. e., it is a gasless reaction, and the adiabatic flame temperature is 3460 K at the stoichiometric mixture ratio. However, this reaction only occurs at high temperatures, above 2000 K. In order to initiate the combustion, a high heat input is needed for ignition. 

Most reactions of bromine are highly exothermic which can cause incandescence or sudden increase in pressure and rupture of reaction flasks. There are a number of cases of explosions documented in the literature. (NFPA. 1986. Fire Protection Guide on Hazardous Materials, 9th ed. Quincy, MA National Fire Protection Association) Reactions of liquid bromine with most metals (or any metal in finely divided state), metal hydrides, carbonyls and nitrides can be explosive. Many oxides and halides of nonmetals, such as nitrogen triiodide or phosphorus trioxide, react explosively or burst into flame in contact with liquid bromine. 

The above reaction is highly exothermic. The stoichiometric proportion of gaseous mixture at equilibrium flame temperature is cooled to 200°C, whereupon the elements combine rapidly to form HCl with over 99% yield. 

Attention also must be given to the explosion and fire hazards presented by combustible organic vapors and combustible gases such as hydrogen and methane. These vapors are readily ignited by static electricity, electrical sparks from most laboratory appliances, open flames, and other highly exothermic reactions. Thus appreciable atmospheric concentrations of combustible vapors should be avoided. 

Reaction of a substance with oxygen in a highly exothermic reaction, usually with a visible flame. 

There are relatively few chemical reactions capable of heating matter to temperatures greater than 3000°K. Table II contains a list of some of these reactions and the theoretical flame temperatures attainable. These reactions have two characteristics in common (1) high exothermic heats of reaction and (2) stable molecular products with low heat capacities, since dissociation consumes energy and results in additional products which must be heated to the flame temperature. 

Theoretical Flame Temperatures op Some Highly Exothermic Reactions (A2)... 

This reaction is exothermic. The heat required to produce gaseous H2O and liquid H2O in this reaction at 25 °C and 1 atm is 242 and 286kJmol", respectively. This reaction proceeds spontaneously at temperatures above 500 °C. At temperatures lower than 500 °C this reaction occurs iu the presence of a snitable catalyst, such as Pt or Pd, or if activated by an electric spark or a flame. The combustion of hydrogen in oxygen prodnces flame temperatures as high as 2800 °C, a technique utilized in oxyhydrogen welding torches. 

SAFETY PROFILE Low toxicity by ingestion. A dangerous fire hazard when exposed to heat or flame can react with oxidizing materials. Moderate explosion hazard in the form of gas when exposed to heat or by chemical reaction. It decomposes violendy at high temperatures and pressures. Dimerization is highly exothermic. 

It appeared that the transfer of heat back from the highly exothermic final stages to the earlier parts was crucial in establishing the stable flame. Most of the products could be accounted for by reactions of types frequently postulated in the combustion of hydrocarbons and their derivatives. Thus, for example, 2-methyl-l 3-dioxacyclopentane could arise by... 

Section 6 deals with the autocatalytic reactions of inorganic and organic compounds with molecular oxygen in the liquid phase, and the highly exothermic processes in the gas phase, collectively known as combustion, which may involve oxygen, other oxidants or decomposition flames and are so important technologically. Catalysis, retardation and inhibition are covered. The kinetic parameters of the elementary steps involved are given, when available, and the reliability of the data discussed. 

A welder uses an exothermic combustion reaction to create a high-temperature flame. 

In neither reaction was the ylide isolated, but its existence was inferred from product isotope distributions. TMO BF ( C or D labelled) was mixed with NaH in a flask and the mixed solids heated with a flame until the highly exothermic reaction initiated. Analysis of the head gas shows the presence of ethylene (0.3-2.5%) and ethane (0.3-2.1%), among other products (Tables 2 and 3). Although hydride methylation to CH and TMO decomposition to DME were the... 

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