Burning chemistry

One of the most readily observed reactions in chemistry is the familiar production of bubbles of a colourless gas when certain metals (for example, iron, zinc) react with dilute acids. Cavendish investigated these reactions rather more than 200 years ago, and found the gas evolved to be the same in each case the gas, later named hydrogen, was much lighter than air and when burned in air produced water. 

Environmental Considerations. Environmental problems in Ziegler chemistry alcohol processes are not severe. A small quantity of aluminum alkyl wastes is usually produced and represents the most significant disposal problem. It can be handled by controlled hydrolysis and separate disposal of the aqueous and organic streams. Organic by-products produced in chain growth and hydrolysis can be cleanly burned. Wastewater streams must be monitored for dissolved carbon, such as short-chain alcohols, and treated conventionally when necessary. 

Chemistry. In direct combustion coal is burned to convert the chemical energy of the coal into thermal energy, ie, the carbon and hydrogen in the coal are oxidized into carbon dioxide and water. 

Electric heat provided by a resistance or by an electric arc can be substituted for the burning of a fuel. Electric furnaces can be designed in a variety of shapes and are more versatile than fuel-heated furnaces. The furnace atmosphere can be controlled independently of the chemistry of the combustion... 

Chemical Properties. The chemistry of the sulfur chlorides has been reviewed (141,142). Sulfur monochloride is stable at ambient temperature but undergoes exchange with dissolved sulfur at 100°C, indicating reversible dissociation. When distilled at its atmospheric boiling point, it undergoes some decomposition to the dichloride, but decomposition is avoided with distillation at ca 6.7 kPa (50 mm Hg). At above 300°C, substantial dissociation to S2 and CI2 occurs. Sulfur monochloride is noncombustible at ambient temperature, but at elevated temperatures it decomposes to chlorine and sulfur (137). The sulfur then is capable of burning to sulfur dioxide and a small proportion of sulfur trioxide. 

The vapor cloud of evaporated droplets bums like a diffusion flame in the turbulent state rather than as individual droplets. In the core of the spray, where droplets are evaporating, a rich mixture exists and soot formation occurs. Surrounding this core is a rich mixture zone where CO production is high and a flame front exists. Air entrainment completes the combustion, oxidizing CO to CO2 and burning the soot. Soot bumup releases radiant energy and controls flame emissivity. The relatively slow rate of soot burning compared with the rate of oxidation of CO and unbumed hydrocarbons leads to smoke formation. This model of a diffusion-controlled primary flame zone makes it possible to relate fuel chemistry to the behavior of fuels in combustors (7). 

The impure iron is made into steel by burning out most of the carbon, sulfur, and phosphorus. Today there are three common furnace types for making steel—the open-hearth furnace (85% of U.S. production), the electric arc furnace (10%), and the Bessemer converter (5%). These furnaces differ in construction but the chemistry is basically similar. 

Chemistry is concerned with the properties of matter, its distinguishing characteristics. A physical property of a substance is a characteristic that we can observe or measure without changing the identity of the substance. For example, a physical property of a sample of water is its mass another is its temperature. Physical properties include characteristics such as melting point (the temperature at which a solid turns into a liquid), hardness, color, state of matter (solid, liquid, or gas), and density. A chemical property refers to the ability of a substance to change into another substance. For example, a chemical property of the gas hydrogen is that it reacts with (burns in) oxygen to produce water a chemical property of the metal zinc is that it reacts with acids to produce hydrogen gas. The rest of the book is concerned primarily with chemical properties here we shall review some important physical properties. 

Sulfur forms several oxides that in atmospheric chemistry are referred to collectively as SOx (read sox ). The most important oxides and oxoacids of sulfur are the dioxide and trioxide and the corresponding sulfurous and sulfuric acids. Sulfur burns in air to form sulfur dioxide, S02 (11), a colorless, choking, poisonous gas (recall Fig. C.1). About 7 X 1010 kg of sulfur dioxide is produced annually from the decomposition of vegetation and from volcanic emissions. In addition, approximately 1 X 1011 kg of naturally occurring hydrogen sulfide is oxidized each year to the dioxide by atmospheric oxygen ... 

The physical properties of the interhalogens are intermediate between those of their parent halogens. Trends in the chemistry of the interhalogen fluorides can be related to the decrease in bond dissociation energy as the central halogen atom becomes heavier. The fluorides of the heavier halogens are all very reactive bromine trifluoride gas is so reactive that even asbestos burns in it. 

Why Do We Need to Know This Material All life on Earth is based on carbon so is the fuel we burn, our food, and the clothes we wear. Therefore, to understand a major part of the everyday world, we need to be familiar with the chemistry of this extraordinary element. Compounds of carbon and hydrogen are the foundation of the petrochemical industry petroleum products are used to generate electricity and to heat our homes. They are also used to make the flexible, strong polymeric and composite materials that make modern communication and transportation possible. 

R. P. Burns Department of Chemistry, University of Manchester, Institute of Science and Technology, Manchester M60 IQD, England... 

Crutzen, P. J. and Andreae, M. O. (1990). Biomass burning in the Tropics impact on atmospheric chemistry and biogeochemical cycles. Science 250, 1669-1678. 

D. T. Burns, A. Townshend, A. H. Carter, Inorganic Reaction Chemistry, Vol. 2, Reactions of the Elements and Their Compounds, Part A AlkaU Metals to Nitrogen, Ellis Hotwood, Chichester, 1981, p. 243. 

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