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Chemical reactions changing speed

Figure 3.89 A chemical reaction changes the speed of an impulse of reactants in a single-channel reactor [38] (by courtesy of VDI-Verlag GmbH). Figure 3.89 A chemical reaction changes the speed of an impulse of reactants in a single-channel reactor [38] (by courtesy of VDI-Verlag GmbH).
A mass spectrometer provides an example of a molecular beam, in this case a beam of molecular ions. Molecular beams are used in many studies of fundamental chemical interactions. In a high vacuum, a molecular beam allows chemists to study the reactions that take place through specifically designed types of collisions. For example, a crossed-beam experiment involves the intersection of two molecular beams of two different substances. The types of substances, molecular speeds, and orientations of the beams can be changed systematically to give detailed information about how chemical reactions occur at the molecular level. Chemists also have learned how to create molecular beams in which the molecules have very little energy of motion. These isolated, low-energy molecules are ideal for studies of fundamental molecular properties. [Pg.308]

Enzymes are exceptionally efficient catalytic proteins which increase the speed of a chemical reaction without themselves undergoing a permanent change. Under optimal conditions, most enzymatic reactions proceed from 10 to 10 times more rapidly than the corresponding non-enzymatic reactions. For example, one molecule of catalase, the enzyme which converts hydrogen peroxide into water and atomic oxygen, is able to deal with approximately 5 million molecules of H2O0 per minute. [Pg.175]

A catalyst is a substance that speeds up a chemical reaction without undergoing a permanent change in its own composition. Catalysts are often but not always noted above or below the arrow in the chemical equation. Since a small quantity of catalyst is sufficient to cause a large quantity of reaction, the amount of catalyst need not be specified it is not balanced like the reactants and products. In this manner, the equation for a common laboratory preparation of oxygen is written... [Pg.118]

In Chapter 3, we defined a new function, the internal energy U, and noted that it is a thermodynamic property that is, dU is an exact differential. As Q was defined in Equation (3.12) as equal to At/ when no work is done, the heat exchanged in a constant-volume process in which only PdV work is done is also independent of the path. For example, in a given chemical reaction carried out in a closed vessel of fixed volume, the heat absorbed (or evolved) depends only on the nature and condition of the initial reactants and of the final products it does not depend on the mechanism by which the reaction occurs. Therefore, if a catalyst speeds up the reaction by changing the mechanism, it does not affect the heat exchange accompanying the reaction. [Pg.43]

Every chemical reaction reaches after a time a state of equilibrium in which the forward and back reactions proceed at the same speed. The law of mass action describes the concentrations of the educts (A, B) and products (C, D) in equilibrium. The equilibrium constant K is directly related to the change in free enthalpy G involved in the reaction (see p.l6) under standard conditions (AG° = - R T In K). For any given concentrations, the lower equation applies. At AG < 0, the reaction proceeds spontaneously for as long as it takes for equilibrium to be reached (i.e., until AG = 0). At AG > 0, a spontaneous reaction is no longer possible (endergonic case see p.l6). In biochemistry, AG is usually related to pH 7, and this is indicated by the prime symbol (AG° or AG ). [Pg.18]

In physics, the time rate of change of motional velocity resulting from changes in a body s speed and/or direction. In biochemistry, acceleration refers to an increased rate of a chemical reaction in the presence of an enzyme or other catalyst. See Catalytic Rate Enhancement Catalytic Proficiency Efficiency Function... [Pg.7]

Catalyst A substance which changes the speed of a chemical reaction but undergoes no permanent change itself. [Pg.225]

A catalytic agent can alter the speed of a chemical action, bat it cannot alter the condition of equilibrium.—Although the speed of a chemical reaction is modified by the presence of a catalytic agent, the final state of equilibrium is not affected. If otherwise, J. H. van t Hoff showed that we could allow these substances to react alternately with and without the catalytic agent this would involve a change in the quantity combined, and the energy thus obtained could be made to do work. This would lead to perpetual motion, which is assumed to be impossible. This deduction has been confirmed experimentally with hydrogen iodide with and without platinum black. Hence, adds W. Nernst, the catalyst must always affect... [Pg.143]

However, the reverse process, in going from speed to distance, involves integration of the rate equation (6.2). In chemistry, the concept of rate is central to an understanding of chemical kinetics, in which we have to deal with analogous rate equations which typically involve the rate of change of concentration, rather than the rate of change of distance. For example, in a first-order chemical reaction, where the rate of loss of the reactant is proportional to the concentration of the reactant, the rate equation takes the form ... [Pg.120]

A Monarchos drives to the finish to win the 2001 Kentucky Derby. His speed is defined as the change in location per unit time (meters per second, m/s). Similarly, the speed, or rate, of a chemical reaction is defined as a change in concentration per unit time (molar per second, M/s). [Pg.471]

Enzymes are large proteins that act as catalysts for biological reactions. A catalyst, as we saw in Section 12.12, is an agent that speeds up the rate of a chemical reaction without itself undergoing change. For example, sulfuric acid catalyzes the reaction of a carboxylic acid with an alcohol to yield an ester (Section 23.14). [Pg.1044]

Catalyst Any matter that is used to change or speed up a chemical reaction without being changed itself or destroyed in the reaction. [Pg.99]

The concentration of metals in atmospheric aerosols and rainwater (Table 7.1) is therefore a function of their sources. This includes both the occurrence of the metals in combustion processes and their volatility, as well as their occurrence in crustal dust and seawater. As a result of this, the size distribution of different metals is very different and depends on the balance of these sources. For a particular metal this distinction is similar in most global locations (Table 7.2), although some variability does occur as wind speed and distance from source exert an influence on the particle size distribution spectrum (Slinn, 1983). Once in the atmosphere particles can change size and composition to some extent by condensation of water vapour, by coagulation with other particles, by chemical reaction, or by activation (when supersaturated) to become cloud or fog droplets (Andreae et al., 1986 Arimoto et al., 1997 Seinfeld and Pandis, 1998). [Pg.166]

Catalysts have been defined as materials that, when present in relatively small amounts, influence the speed of a chemical reaction while not undergoing any permanent chemical change. A catalyst is generally considered to speed up a reaction. It also can slow it down. [Pg.35]

A catalyst is a substance which influences the speed of a chemical reaction without itself undergoing any chemical change at the end of the reaction. ... [Pg.252]


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See also in sourсe #XX -- [ Pg.106 , Pg.107 ]




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