Stoichiometric ratios

The stoichiometric ratio is the proportion of fuel and oxidizer that results in optimal combustion and maximum heat release. The optimal ratio is deter- 

A mixture below it stoichiometric ratios is described as lean. A mixture above its stoichiometric ratio is described as rich. A lean mixture has extra oxygen along with the combustion products and a rich mixture has fuel remaining with the combustion products. 

Fuel-air mixtures at or around stoichiometric concentration have the lowest autoignition temperature, lowest minimum ignition energies, and highest burning velocities. 

Heat can be transferred by conduction, convection, and radiation. Conduction is heat transfer through a solid. Convection is heat transfer in a fluid. Radiation is heat transfer by electromagnetic radiation and does not require a transfer medium. Heat transfer is always from hot to cold. 

The main mechanisms of heat transfer in a hydrocarbon are thermal radiation and direct flame contact. Heat transfer to personnel will cause burns. Heat transfer to equipment and structures can lead to failure of hydrocarbon containing equipment, which can further feed the fire. 

Finally, the variation of the glass transition temperature for both systems (DGEBA-IPDA or DGEBA-DETA) versus the stoichiometric ratio (a/e) is reported (e.g., see Fig. 7.6) for either pure or modified materials. Usually, as the functionalities of epoxy and amine monomer were well defined, mixing materials at the stoichiometric ratio of 1 led to the formation of the most crosslinked network having the highest glass transition temperature. From Fig. 7.6 it can be 

In all our systems the corresponding ether bands (1120 cm ) were also found. 

When epoxy-amine prepolymers were applied on metallic substrates, interphases between the coating part, having the bulk properties, and the metallic surface were created. Amine chemisorption onto oxidic or hydroxidic metallic surfaces, concomitantly with partial dissolution of the surface oxide (and/or hydroxide) on the metal substrate, was observed, according to the basicity characteristics of the amine monomers (pfC, 10). Then it could be assumed that either  

We acknowledge the Perkin-Elmer Instruments team from Lyons (and particularly Dr. P. Delmont), for their help in making the x-FTIR maps. Also, we thank the crystallographic group of Claude Bernard University from Lyons 1 (principally D. Merle, Prof Perrin, and Dr. Thozet) for doing XRD analyses and for their helpful discussion. 

Bouchet, S. Bentadjine, International Journal of Adhesion and Adhesives, 2002, 22, 431 41. 

---

Although the flowsheet shown in Fig. 4.7a is very attractive, it is not practical. This would require careful control of the stoichiometric ratio of decane to chlorine, taking into account both the requirements of the primary and byproduct reactions. Even if it was possible to balance out the... 

Stoichiometry is the composition of the air-fuel mixture required to obtain complete combustion. The stoichiometric ratio, r, is the quotient of the respective masses, and m, of air and fuel arranged in the stoichiometric conditions ... 

If one imagine.s that the fuel is used in the liquid state in the form of droplets —as in the case of fuel injection— the specific energy of the motor fuel (SE) is expressed in kilojoules per kilogram of air utilized, under predetermined conditions of equivalence ratio (stoichiometry for example). The SE is none other than the NHY /r quotient where r represents the previously defined stoichiometric ratio. 

The diesel engine operates, inherently by its concept, at variable fuel-air ratio. One easily sees that it is not possible to attain the stoichiometric ratio because the fuel never diffuses in an ideal manner into the air for an average equivalence ratio of 1.00, the combustion chamber will contain zones that are too rich leading to incomplete combustion accompanied by smoke and soot formation. Finally, at full load, the overall equivalence ratio... 

Thermal energy in flame atomization is provided by the combustion of a fuel-oxidant mixture. Common fuels and oxidants and their normal temperature ranges are listed in Table 10.9. Of these, the air-acetylene and nitrous oxide-acetylene flames are used most frequently. Normally, the fuel and oxidant are mixed in an approximately stoichiometric ratio however, a fuel-rich mixture may be desirable for atoms that are easily oxidized. The most common design for the burner is the slot burner shown in Figure 10.38. This burner provides a long path length for monitoring absorbance and a stable flame. 

Acetylene-Based Routes. Walter Reppe, the father of modem acetylene chemistry, discovered the reaction of nickel carbonyl with acetylene and water or alcohols to give acryUc acid or esters (75,76). This discovery led to several processes which have been in commercial use. The original Reppe reaction requires a stoichiometric ratio of nickel carbonyl to acetylene. The Rohm and Haas modified or semicatalytic process provides 60—80% of the carbon monoxide from a separate carbon monoxide feed and the remainder from nickel carbonyl (77—78). The reactions for the synthesis of ethyl acrylate are... 

Where T)is flame temperature in K MC is moisture content of the waste, expressed on a total weight basis SR is defined as stoichiometric ratio or moles O2 avadable/moles O2 required for complete oxidation of the carbon, hydrogen, and sulfur in the fuel, ie, 1/SR = equivalence ratio and is temperature of the combustion air, expressed in K. In Fnglish units, this equation is as follows ... 

Figure 4 illustrates the trend in adiabatic flame temperatures with heat of combustion as described. Also indicated is the consequence of another statistical result, ie, flames extinguish at a roughly common low limit (1200°C). This corresponds to heat-release density of ca 1.9 MJ/m (50 Btu/ft ) of fuel—air mixtures, or half that for the stoichiometric ratio. It also corresponds to flame temperature, as indicated, of ca 1220°C. Because these are statistical quantities, the same numerical values of flame temperature, low limit excess air, and so forth, can be expected to apply to coal—air mixtures and to fuels derived from coal (see Fuels, synthetic). 

Examples of the hydroquinone inclusion compounds (91,93) are those formed with HCl, H2S, SO2, CH OH, HCOOH, CH CN (but not with C2H 0H, CH COOH or any other nitrile), benzene, thiophene, CH, noble gases, and other substances that can fit and remain inside the 0.4 nm cavities of the host crystals. That is, clathration of hydroquinone is essentially physical in nature, not chemical. A less than stoichiometric ratio of the guest may result, indicating that not all void spaces are occupied during formation of the framework. Hydroquinone clathrates are very stable at atmospheric pressure and room temperature. Thermodynamic studies suggest them to be entropic in nature (88). 

When equal amounts of solutions of poly(ethylene oxide) and poly(acryhc acid) ate mixed, a precipitate, which appears to be an association product of the two polymers, forms immediately. This association reaction is influenced by hydrogen-ion concentration. Below ca pH 4, the complex precipitates from solution. Above ca pH 12, precipitation also occurs, but probably only poly(ethylene oxide) precipitates. If solution viscosity is used as an indication of the degree of association, it appears that association becomes mote pronounced as the pH is reduced toward a lower limit of about four. The highest yield of insoluble complex usually occurs at an equimolar ratio of ether and carboxyl groups. Studies of the poly(ethylene oxide)—poly(methacryhc acid) complexes indicate a stoichiometric ratio of three monomeric units of ethylene oxide for each methacrylic acid unit. 

Foi lineal step-giowth, the numbei-aveiage degree of polymerization, is given by equation 7, where r = j, the stoichiometric ratio of the... 

Liquid-phase chlorination of butadiene in hydroxyhc or other polar solvents can be quite compHcated in kinetics and lead to extensive formation of by-products that involve the solvent. In nonpolar solvents the reaction can be either free radical or polar in nature (20). The free-radical process results in excessive losses to tetrachlorobutanes if near-stoichiometric ratios of reactants ate used or polymer if excess of butadiene is used. The "ionic" reaction, if a small amount of air is used to inhibit free radicals, can be quite slow in a highly purified system but is accelerated by small traces of practically any polar impurity. Pyridine, dipolar aptotic solvents, and oil-soluble ammonium chlorides have been used to improve the reaction (21). As a commercial process, the use of a solvent requites that the products must be separated from solvent as well as from each other and the excess butadiene which is used, but high yields of the desired products can be obtained without formation of polymer at higher butadiene to chlorine ratio. 

Explosively violent hydrolysis can occur if an excess of a strong acid (H2SO4, HNO, or HCl) is added to hydrogen cyanide. The reaction is fastest at or near stoichiometric ratios, eg, 1 to 2 moles H2SO4 per mole HCN, and can cause severe equipment damage if confined. 

It is not necessary for a compound to depart from stoichiometry in order to contain point defects such as vacant sites on the cation sub-lattice. All compounds contain such iirndirsic defects even at the precisely stoichiometric ratio. The Schottky defects, in which an equal number of vacant sites are present on both cation and anion sub-lattices, may occur at a given tempe-ramre in such a large concentration drat die effects of small departures from stoichiometry are masked. Thus, in MnOi+ it is thought that the intrinsic concentration of defects (Mn + ions) is so large that when there are only small departures from stoichiometry, the additional concentration of Mn + ions which arises from these deparmres is negligibly small. The non-stoichiometry then varies as in this region. When the departure from non-stoichio-... 

The accuracy in RBS results is -3% for areal densities and better than 1% for stoichiometric ratios. This high accuracy is obtained only when all relevant quantities are measured or evaluated carefully. Pitfalls which often prevent RBS from achieving its full accuracy are described elsewhere [3.129]. Calibration can be achieved by measuring standards obtained by either implanting into or depositing on a light element (silicon) a known amount of a much heavier element (e.g. Ta or Sb). 

In cases where the reactants involved are not present in the proper stoichiometric ratios, the limiting reactant will have to be determined and the excess amounts of the other reactants calculated. It is safe to assume that unconsumed reactants and inert components exit with the products in their original forms. Consider the following example. 

Single reaction substance A Reactants in their stoichiometric ratios ... 

From Eq. (4-la) the stoichiometric concentration of methane in oxygen is 1 part in 3 = 33.3 mole percent methane. From Eq. (4-lb) the approximate stoichiometric concentration of methane in air is 1 part in 3 -E (158/21) = 9.5 mole percent methane. Tims, a mixtnre of 15 mole percent methane in oxygen has a stoichiometric ratio (p = 15/33.3 = 0.45 (lean), while the same methane concentration in air has a stoichiometric ratio (p = 15/9.5 = 1.58 (rich). 

For paraffins the stoichiometric ratio decreases as the nnmber of carbon atoms increases. Using a more precise calcnlation (which inclndes other species snch as CO, OH, etc.) than that shown in Eq. (4-lb), methane s stoichiometric ratio in air is 9.48 mole percent, propane s is 4.01 mole percent, and hexane s is 2.16 mole percent. Hydrogen, which combines with oxygen to form only water, has a stoichiometric ratio of 29.6 mole percent in air. 

Stoichiometric ratio The precise ratio of air (or oxygen) and flammable material which would allow all oxygen present to combine with all flammable material present to produce fully oxidized products. 

---