Releasing Energy

The temperature of chemicals changes as they react with each other. Heat releases or is absorbed into the compound during a chemical reaction. The compound becomes warm or hot when heat releases. Scientists call this an exothermic reaction. Most of the chemical reactions that occur in nature are slow exothermic reactions. They take place so slowly that it is difficult to notice the release of heat. Exothermic reactions are often easy to see when fuels burn. Energy releases 

An exothermic reaction occurs when vinegar removes the coating from a steel wool pad. When the steel meets oxygen, oxidation occurs, releasing heat. 

Reacting chemicals become cooler when heat is absorbed. Scientists call this an endothermic reaction. Photosynthesis is one of the few natural endothermic reactions. Photosynthesis occurs when plants convert or change sunlight, carbon dioxide, and water into oxygen and food. Plants actually get a little bit cooler during photosynthesis. 

Cold packs, used by doctors and athletes, lower the temperature of an injury. A cold pack contains two chemicals. The chemicals react with each other when they are mixed. The endothermic reaction absorbs heat from the injured part of the body. It helps to cool the body down. 

Athletes use cold packs that do not have to be frozen. To get the pack to be cold, the athlete smashes the pack on a hard surface. The chemicals inside the pack mix together, causing them to become very cold. 

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AES ARABS Auger electron spectroscopy [77, 112-114, 117] Angle-resolved AES [85, 115] An incident high-energy electron ejects an inner electron from an atom an outer electron (e.g., L) falls into the vacancy and the released energy is given to an ejected Auger electron Surface composition... 

Table 20. Calculated Crystal Densities and Releasable Energy Density for HEDCs and In-Service Explosives...

RocketPropella.nts, Liquid propellants have long been used to obtain maximum controUabiUty of rocket performance and, where required, maximum impulse. Three classes of rocket monopropellants exist that differ ia the chemical reactions that release energy (/) those consisting of, eg, hydrogen peroxide, ethylene oxide, C2H4O and nitroethane, CH2CH2NO2 that can undergo internal oxidation—reduction reactions (2) those... 

Physiological Role of Citric Acid. Citric acid occurs ia the terminal oxidative metabolic system of virtually all organisms. This oxidative metabohc system (Fig. 2), variously called the Krebs cycle (for its discoverer, H. A. Krebs), the tricarboxyUc acid cycle, or the citric acid cycle, is a metaboHc cycle involving the conversion of carbohydrates, fats, or proteins to carbon dioxide and water. This cycle releases energy necessary for an organism s growth, movement, luminescence, chemosynthesis, and reproduction. The cycle also provides the carbon-containing materials from which cells synthesize amino acids and fats. Many yeasts, molds, and bacteria conduct the citric acid cycle, and can be selected for thek abiUty to maximize citric acid production in the process. This is the basis for the efficient commercial fermentation processes used today to produce citric acid. 

The assignment of degrees in the reactivity category is based upon the susceptibility of materials to release energy either by themselves or in combination with water. Rre exposure was one of the factors considered along with conditions of shock and pressure. 

The released energy might result from the wanted reaction or from the reaction mass if the materials involved are thermodynamically unstable. The accumulation of the starting materials or intermediate products is an initial stage of a runaway reaction. Figure 12-6 illustrates the common causes of reactant accumulation. The energy release with the reactant accumulation can cause the batch temperature to rise to a critical level thereby triggering the secondary (unwanted) reactions. Thermal runaway starts slowly and then accelerates until finally it may lead to an explosion. 

Chemical explosions are uniform or propagating explosions. An explosion in a vessel tends to be a uniform explosion, while an explosion in a long pipe is a propagating explosion. Explosions are deflagrations or detonations. In a deflagration, the burn is relatively slow, for hydrocarbon air mixtures the deflagration velocity is of the order of 1 m/s. In contrast, a detonation flame shock front is followed closely by a combustion wave that releases energy to sustain the shock wave. A... 

It is user friendly and possesses a graphical user interface for developing the flow paths, ventilation system, and initial conditions. The FIRIN and CFAST modules can be bypassed and temperature, pressure, gas, release energy, mass functions of time specified. FIRAC i.s applicable to any facility (i.e., buildings, tanks, multiple rooms, etc,) with and without ventilation systems. It is applicable to multi species gas mixing or transport problems, as well as aerosol transport problems, FIRAC includes source term models for fires and limitless flow paths, except the FlRlN fire compartment limit of to no more than three... 

This result should be vahd for sufficiently high density 0 where correlations, brought about by the mutual avoidance of the chains, are negligible. Due to the recombination-scission process a polydisperse solution of living polymers should absorb or release energy as the temperature is varied. This is reflected by the specific heat Cy, which can be readily obtained from Eq. (9) as a derivative of the internal energy U... 

In practice, overpressures in one case might very well be only one-fifth of those predicted by the method and close to the predicted value in another case. This inherent inaccuracy limits the value of this method in postaccident analysis. Even when overpressures can be accurately estimated from blast damage, released energy can only be estimated within an order of magnitude. 

Both of the reactions, radical combination and Diels-Alder cycloaddition, cause new bonds to be made. Bond making normally releases energy. Why then are the barriers for the two reactions so different (Hint Consider the nel bond making/bond breaking in the two reactions.)... 

To release energy, the electrons can be removed from glucose and used to create ATP, a molecule that supplies a cell s short-term energy needs. This latter occurs in a series of reactions known as respiration. (Body heat is a by-product of these reactions.) The most efficient respiration reactions are those that use oxygen to accept the electrons removed from glucose. Thus respiration is the reverse of photosynthe-... 

Some neutral atoms can gain electrons, forming negative ions. Thus a neutral fluorine atom can add an electron to form a negative ion, F-. This change, for fluorine atoms, does not require the input of energy it releases energy ... 

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