Ozone forests

Note The detection limits for the various peroxides are from 0.5 to 2 pg substance per chromatogram zone [1]. The reaction works best when the reagent solution is 3-5 days old later the background absorption increases. The background coloration that is produced on drying in a stream of cold air can be largely avoided by drying the plate after dipping in the absence of oxygen, first with a moist and then with a stream of dry nitrogen [1].  [c.369]

Electrostatic and orbital interactions may steer reaction toward either carbon or oxygen. First, examine the electrostatic potential map for cyclohexanone lithium enolate. Which atom is more negatively charged, carbon or oxygen Is the difference significant If it is, what would be the favored mode of addition Does either methylation or silylation appear to be guided by electrostatics Explain.  [c.168]

Many processes are based on an oxidation step for which air would be the first obvious source of oxygen. A partial list would include acetic acid, acetylene, acrylic acid, acrylonitrile, carbon black, ethylene oxide, formaldehyde, maleic anhydride, nitric acid, phenol, phthalic anhydride, sulfuric acid, titanium dioxide, vinyl acetate, and vinyl chloride. Clearly, because the nitrogen in the air is not required by the reaction, it must be separated at some point. Because gaseous separations are difiicult, the nitrogen is normally separated using a purge, or alternatively, the reactor is forced to as high a conversion as possible to avoid recycling. If a purge is used, the nitrogen will carry with it process materials, both feeds and products, and will probably require treatment before final discharge. If the air for the oxidation is substituted by pure oxygen, then, at worst, the purge will be very much smaller. At best, it can be eliminated altogether. Of course, this requires an air separation plant upstream of the process to provide the pure oxygen. However, despite this disadvantage, very significant benefits can be obtained, as the following example shows.  [c.283]

If the composition of the waste stream is known, then the theoretical oxygen demand can be calculated from the appropriate stoichiometric equations. As a first level of approximation, we can assume that this theoretical oxygen demand would be equal to the COD. Then, experience with domestic sewage indicates that the average ratio of COD to BOD will be on the order 1.5 to 2. The following example will help to clarify these relationships.  [c.309]

Solution First, calculate the theoretical oxygen demand from the equation that represents the overall oxidation of the acetone  [c.309]

CH2=CHC = CCH = CH2. a colourless liquid which turns yellow on exposure to the air it has a distinct garlic-like odour b.p. 83-5°C. Manufactured by the controlled, low-temperature polymerization of acetylene in the presence of an aqueous solution of copper(I) and ammonium chlorides. It is very dangerous to handle, as it absorbs oxygen from the air to give an explosive peroxide. When heated in an inert atmosphere, it polymerizes to form first a drying oil and finally a hard, brittle insoluble resin. Reacts with chlorine to give a mixture of chlorinated products used as drying oils and plastics.  [c.145]

Finally, the determination of the induction period (NF M 07-012) also reveals the potential of gum formation during storage. The fuei sampie is contained in a bomb filled with oxygen at 100°C, under a pressure of 7 bar and the oxygen pressure is monitored with time. The time corresponding to the first drop in pressure is noted, symptomatic of incipient oxidation. If no further events take place, the test is stopped after 960 minutes. This time corresponds thus to the maximum induction period.  [c.242]

The Fischer-Tropsch reaction is essentially that of Eq. XVIII-54 and is of great importance partly by itself and also as part of a coupled set of processes whereby steam or oxygen plus coal or coke is transformed into methane, olefins, alcohols, and gasolines. The first step is to produce a mixture of CO and H2 (called water-gas or synthesis gas ) by the high-temperature treatment of coal or coke with steam. The water-gas shift reaction CO + H2O = CO2 + H2 is then used to adjust the CO/H2 ratio for the feed to the Fischer-Tropsch or synthesis reactor. This last process was disclosed in 1913 and was extensively developed around 1925 by Fischer and Tropsch [268].  [c.730]

The hydration of more inert ions has been studied by O labelling mass spectrometry. 0-emiched water is used, and an equilibrium between the solvent and the hydration around the central ion is first attained, after which the cation is extracted rapidly and analysed. The method essentially reveals the number of oxygen atoms that exchange slowly on the timescale of the extraction, and has been used to establish the existence of the stable [1 10304] cluster in aqueous solution.  [c.568]

Thennal dissociation is not suitable for the generation of beams of oxygen atoms, and RF [18] and microwave [19] discharges have been employed in this case. The first excited electronic state, 0( D), has a different spin multiplicity than the ground 0( P) state and is electronically metastable. The collision dynamics of this very reactive state have also been studied in crossed-beam reactions with a RF discharge source which has been  [c.2065]

Figure C1.5.17.(A) Enzymatic cycle of cholesterol oxidase, which catalyses tire oxidation of cholesterol by molecular oxygen. The enzyme s naturally fluorescent FAD active site is first reduced by a cholesterol substrate, Figure C1.5.17.(A) Enzymatic cycle of cholesterol oxidase, which catalyses tire oxidation of cholesterol by molecular oxygen. The enzyme s naturally fluorescent FAD active site is first reduced by a cholesterol substrate,
The nonrelativistic states are described at the first-order configuration interaction level using a six orbital, eight electron, active space with the oxygen Is orbital kept doubly occupied. The molecular orbitals were constructed from a state-averaged multiconfigurational self-consistent field procedure [31] using an extended atomic orbital basis on oxygen and hydrogen. The details of this description can be found in [30].  [c.465]

Energy is evolved in each case. The table clearly indicates that the electron affinity falls with the increasing size of the atom. The anomalous value for fluorine is explained on the grounds that since the fluorine atom is small, the incoming electron encounters strong repulsion by the nine electrons already closely shielding the nucleus. In each case, the ion produced by electron addition is larger than the atom from which it was formed. After the addition of the first electron, subsequent electron addition must take place against the repulsion of a negatively-charged ion. Two-electron affinities are known in only a few cases. The values for oxygen and sulphur are given in Table 2.5.  [c.33]

A full treatment of this important—and indeed exciting—area of chemistry belongs to physical chemistry. Here, we are chiefly concerned with two fundamental questions about a chemical reaction—why does it proceed, and why does it give one product rather than another There are many processes, both physical and chemical, which proceed spontaneously. Consider first two flasks, one containing only oxygen and the other only nitrogen, which are connected by opening a tap. The two gases mix spontaneously and the mixture is eventually uniform in both flasks—there has been no chemical reaction but spontaneous mixing has occurred. When anhydrous aluminium chloride is added to water the reaction described on p. 45 occurs with the evolution of a great deal of heat— a strongly exothermic spontaneous reaction. Addition of solid ammonium nitrate to water leads to solution with the absorption of heat—a spontaneous endothermic reaction. These reactions are all spontaneous, but clearly there are wide differences in the apparent energy changes involved.  [c.62]

Sheet aluminium can be given a colour by a similar process. The aluminium is first made the anode in a bath of chromic acid (p. 377) when, instead of oxygen being evolved, the aluminium becomes coated with a very adherent film of aluminium oxide which is very adsorbent. If a dye is added to the bath the oxide film is coloured, this colour being incorporated in a film which also makes the remaining aluminium resistant to corrosion. This process is called anodising aluminium.  [c.151]

Helium has two important scientific uses. First, liquid helium is used to realise very low temperatures, in order to study peculiar phenomena which occur near the absolute zero—cryogenics. Some metals attain enormously high electrical conductivity when cooled down to near absolute zero, and hence powerful electro-magnets can be made using very small coils cooled in liquid helium. Secondly, it is used in gas thermometers for low temperature measurement. Further, any of the rare gases may be used to give an inert atmosphere for handling very reactive metals for example an atmosphere of argon is used in the preparation of titanium and in metallurgical processes, involving this metal, because it is attacked at red heat by both oxygen and nitrogen.  [c.357]

The process of extraction requires first smelting (to obtain the crude metal) and then refining. In smelting, iron ore (usually an oxide) is mixed with coke and limestone and heated, and hot air (often enriched with oxygen) is blown in from beneath (in a blast furnace). At the lower, hotter part of the furnace, carbon monoxide is produced and this is the essential reducing agent. The reduction reactions occurring may be represented for simplicity as  [c.391]

The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope.  [c.443]

The probable mechanism of this change is first proton addition to one oxygen atom of the pinacol to give (I), which loses water to give the carbonium ion (II). I he group R then migrates to give the isomeric ion (III), which loses a proton, giving the pinacolone (IV ).  [c.152]

The first method should be used, however, by experienced students, as it has the advantage that the initial reaction of the compound with the sodium as the cold mixture is warmed can be observed, and frequently gives an indication of the general nature of the compound thus a vigorous reaction in the cold, or immediately on gentle warming, may indicate an acidic substance, whereas a vigorous reaction after the mixture has been gently heated may indicate a compound rich in oxygen evolution of violet vapour of iodine indicates a substance rich in iodine, etc.  [c.322]

The oxygen used in the combustion is supplied by a small cylinder (120 Atm.) fitted with a pressure reduction valve, pressure gauge (to avoid the risk of the cylinder becoming exhausted during an actual determination) and fine control knob. It is important that the valve is kept free from oil or grease of any kind. In order to ensure the complete purity of the oxygen it is first passed through a purification train.  [c.467]

In practice the closed tubes are carefully polished to remove all grease, moisture, etc. and are then allowed to stand for a definite period of time in the air, to pick up a definite amount of water vapour— this process is known as maturing. Unless the atmospheric conditions change very considerably during the experiment (about 2 hours), the amount of water vapour deposited on the polished tubes before and after the combustion will be the same and any systematic error will have been avoided. Unless the tubes have been used in the combustion tube burning-out process, and so are full of oxygen, they must be filled with oxygen before weighing by connecting to the apparatus (both furnace and mortar being cold) and passing oxygen through for 20 minutes, (It is very important not to forget this when a spent absorption tube is replaced by a freshly-packed one.)  [c.475]

Ozone [10028-15-6], O, is an aUotropic form of oxygen first recognized as a unique substance in 1840 (1). Its pungent odor is detectable at - O-Ol ppm. It is thermally unstable and explosive in the gas, Hquid, and soHd phases. In addition to being an excellent disinfectant, ozone is a powerful oxidant not only thermodynamically, but also kineticaHy, and has many useful synthetic appHcations in research and industry. Its strong oxidizing and disinfecting properties and its innocuous by-product, oxygen, make it ideal for the treatment of water. Indeed, the most important appHcation of ozone is in the treatment of drinking water, which began in Europe in 1903 in the mid-1990s, there are well over 2000 such water-treatment installations, primarily in Europe. The treatment of swimming pool water was also developed in Europe during the 1960s (see Water, treatment OF swimming pools, spas, and hottubs). Another important ozone appHcation is for odor control in industrial processes and municipal wastewater-treatment plants. Ozone also is used on a large scale for the treatment of municipal secondary effluents (see Water, municipal water treatment). Industrial high quaHty water suppHes are also treated with ozone (see Water, industrial water treatment). In addition, ozone has appHcations in the treatment of cooHng-tower water and in pulp bleaching. Advanced oxidation processes employing ozone in combination with uv, and/or soHd catalysts such as Ti02 gready improve the reactivity of ozone toward  [c.490]

Oxygen first liquefied by L. Cailletet and R. Pictet (independently).  [c.601]

The classic explanation for the presence of an activation energy in the case where dissociation occurs on chemisorption is that of Lennard-Jones [113] and is illustrated in Fig. XVIII-12 for the case of O2 interacting with an Ag(llO) surface. The curve labeled O2 represents the variation of potential energy as the molecule approaches the surface there is a shallow minimum corresponding to the energy of physical adsorption and located at the sum of the van der Waals radii for the surface atom of Ag and the O2 molecule. The curve labeled O + O, on the other hand, shows the potential energy variation for two atoms of oxygen. At the right, it is separated from the first curve by the O2 dissociation energy of some 120 kcal/mol. As the atoms approach the surface, chemical bond formation develops, leading to the deep minimum located at the sum of the covalent radii for Ag and O. The two curves cross, which means that O2 can first become physically adsorbed and then undergo a concerted dissociation and chemisorption process, leading to chemisorbed O atoms (see Ref. 113a for a more general diagram). In this type of sequence, the molecularly adsorbed species is known as a precursor state (see Refs. 115 and 116).  [c.703]

The first step consists of the molecular adsorption of CO. The second step is the dissociation of O2 to yield two adsorbed oxygen atoms. The third step is the reaction of an adsorbed CO molecule with an adsorbed oxygen atom to fonn a CO2 molecule that, at room temperature and higher, desorbs upon fomiation. To simplify matters, this desorption step is not included. This sequence of steps depicts a Langmuir-Hinshelwood mechanism, whereby reaction occurs between two adsorbed species (as opposed to an Eley-Rideal mechanism, whereby reaction occurs between one adsorbed species and one gas phase species). The role of surface science studies in fomuilating the CO oxidation mechanism was prominent.  [c.953]

Chlorine reacts with most elements, both metals and non-metals except carbon, oxygen and nitrogen, forming chlorides. Sometimes the reaction is catalysed by a trace of water (such as in the case of copper and zinc). If the element attacked exhibits several oxidation states, chlorine, like fluorine, forms compounds of high oxidation state, for example iron forms iron(III) chloride and tin forms tin(IV) chloride. Phosphorus, however, forms first the trichloride, PCI3, and (if excess chlorine is present) the pentachloride PCI5.  [c.322]

Unexpectedly we find that the bromate(V) ion in acid solution (i.e. effectively bromic(V) acid) is a more powerful oxidising agent than the chlorate(V) ion, CIO3. The halates(V) are thermally unstable and can evolve oxygen as one of the decomposition products. Potassium chlorate(V), when heated, first melts, then resolidifies due to the formation of potassium chlorate(VII) (perchlorate)  [c.340]

Once the atoms arc defined, the bonds between them arc specified in a bond block. Each line of this block specifies which two atoms are bonded, the multiplicity of the bond (the bond type entry) and the stereo configuration of the bond (there arc also three additional fields that arc unused in Molfiles and usually set to 0). The indices of the atoms reflect the order of their appearance in the atom block. In the example analyzed, V relates to the first carbon atom (see also Figure 2-24). "2" to the second one, 3" to oxygen atom, etc. Then the two first lines of the bond block of the analyzed file (Figure 2-29) describe the single bond between the two carbon atoms C1-C2 and the double bond C2=0-5, respectively.  [c.50]

Luluff used depends on the nature of the system under investigation. For example, in the fir.-.l-row elements the 2p valence orbitals approach closer to the nucleus than the com-[la ruble 3p orbitals in the second-row elements (the latter are repelled by the lower 2p stales). Thus elements such as silicon or sulphur usually have softer pseudopotentials I ban their first-row equivalents carbon and oxygen. Everything else being equal, a higher aitiiff is consequently required for the latter and hence more plane waves in the expansion lie. more reciprocal lattice vectors, G). Note that in the plane wave expansion the basis fii.nctions are not associated with particular atoms but are defined over fhe whole cell Ubis also removes the problem of basis-set superposition errors as an additional benefit), rill coefficients fl, k+G are obtained by following the usual density functional scheme an initial guess is made of the electron density variation p(r), the Kohn-Sham and overlap matrices are constructed, diagonalisation gives the eigenfunctions and eigenvectors (and thus the coefficients a) from which the Kohn-Sham orbitals can be constructed and hence Ibe density for the next iteration.  [c.175]

I his approach to the calculation of free energy differences. Equation (11.6), is gener attributed to Zwanzig [Zwanzig 1954]. To perform a thermodynamic perturbation calculal we must first define and and then run a simulation at the state X, forming ensemble average of exp[—(jfy — x)/ bT] as we proceed. Analogously, we could ru simulation at the state Y and obtain the ensemble average of exp[-(jfx - JifY)/kBT]- T1 if X corresponds to ethanol and Y to ethane thiol, the free energy difference could obtained from a simulation of ethanol in a periodic box of water as follows. For e configuration we calculate the value of the energy for every instantaneous conformat of ethanol in which the oxygen atom is temporarily assigned the potential energy p meters of sulphur. Alternatively, we could simulate ethane thiol and for each configurat calculate the energy of the system in which the sulphur is mutated into oxygen.  [c.581]

The manometer D is connected with impregnated pressure-tubing, and by a glass-to-glass joint, with the side-arm F of a U -tube (each limb being about i cm. in diameter and 12 cm. long). Before filling, the U-tube should be washed with distilled water, alcohol, then ether and finally dried in an oven. The first limb of the U-tube contains soda-lime (B.D.H. Micro-analytical reagent grade Carbasorb is very convenient) whose purpose is to remove any carbon dioxide from the oxygen stream. A drawback of the soda-lime is that it readily takes up water vapour (a little comes from the pressure gauge) becoming first sticky and then forming a hard impermeable crust that greatly slows the oxj gen stream. This difficulty may be overcome by putting a small quantity of magnesium perchlorate (Anhydrone—M.A.R. grade) in the top of the U-tube limb this also absorbs water, but tends to contract as it does so, drawing away from the wall of the tube and hence not impeding the oxygen flow. Thus in filling the U-tube a small plug of glass wool is put at the bottom ofthe limb, the limb two-thirds filled with soda-lime, a further plug of glass wool inserted, the top third of the tube filled with magnesium perchlorate and topped with a plug of glass wool that comes just opposite the side-arm. The open end of the limb which projects (5 cm.) above the side-arm is then sealed off. Sealing off the limb has been found to be most satisfactoiy, as stoppers, taps, e/c., tend to leak or to give other trouble. (Glass stoppers, each previously ground to fit its own neck, are reasonably satisfactoiy if carefully sealed with glass cement for subsequent recharging, the cement is softened by warming and the stopper released.) After being used  [c.468]

Another small asbestos plug is then inserted to confine the lead peroxide (it s very important that the lead peroxide is not tamped down or it will almost completely prevent passage of gas through the tube) followed by a 30 mm. roll of silver gauze, treated in the same way as the first one inserted. This is the main halogen-absorbent, the one already inserted sendng as a trap (at 180 ) to catch any halogen lost by the hot (680°) silver halide first formed. Next about 25-30 mm. of ignited asbestos is added this is known as a " choking plug" as it is this clement of filling that offers the major part of the resistance to the flow of oxygen in the apparatus. The exact dimensions and compression of the choking plug are determined by trial and error. The amount of asbestos is so adjusted that, when the combustion tube is completely packed, the apparatus assembled, the absorption tubes in place, the furnace and thermostatic mortar at their equilibrium temperatures, and also when there is a pressure of 60 mm,/water registered on the pressure gauge and a reduced head of about 20 mm. of water on the Mariotte bottle, the rate of flow of oxygen through the apparatus is about 5 ml. per min. It is essential to have the furnace and mortar on while this adjustment is being made as temperature greatly affects the rate at w hich gas will flow at a given pressure difference (hot tubes generally run noticeably faster than cold).  [c.473]

See pages that mention the term Ozone forests : [c.289]    [c.37]    [c.406]    [c.1099]    [c.2557]    [c.567]    [c.32]    [c.239]    [c.354]    [c.181]    [c.148]    [c.232]    [c.325]    [c.126]    [c.591]    [c.644]    [c.469]    [c.472]   
Fundamentals of air pollution (1994) -- [ c.113 , c.119 , c.121 ]