Reversibility, chemical meaning

The double arrow in the chemical equation above indicates that the reaction is reversible. This means that while some hydrochloric acid molecules are breaking down into hydrogen and chlorine ions, some ions are also combining to produce hydrochloric acid. The same ongoing, continuous process also occurs to the ammonia molecules. Some ammonia molecules accept a hydrogen ion to become an ammonium ion while some ammonium ions give up a hydrogen ion to become an ammonia molecule. 

Trivially, photo-excitation will drastically enhance the oxidation potential of the flavin chromophore and might give rise to a great variety of reversible chemical reactions, depending on the structure of the environment and/or the pathway of potential e - as well as H -conductivity. It must be emphasized, that the oxidative action of the flavin triplet Tj is by no means confined to 1 e -uptake from suitable aromatic... 

Ion energy and flux represent another important aspect in achieving and controlling selectivity. Because ion bombardment generally imparts different degrees of damage to different materials, etch selectivity can often be varied and even reversed from that obtained via chemical means. In... 

The mean reaction time during a reaction varies as the concentration varies if the reaction is not a first-order reaction. Expressions of mean reaction time of various types of reactions are listed in Table 1-2. In practice, half-lives are often used in treating radioactive decay reactions, and mean reaction times are often used in treating reversible chemical reactions. 

A sensor is a device able to respond to the presence of one or many given substances in a more-or-less selective way, by means of a reversible chemical interaction it may be employed for qualitative or quantitative determinations (Cattrall, 1997). All sensors are composed of two parts the responsive region and the transducer. The responsive region is responsible for sensitivity and selectivity of the sensor, while the transducer converts energy from one to another form, providing a signal which is informative about the system analyzed. Usually, basic signalprocessing electronics, and control and display units complete the device. 

A concept that is critical in the complex evaluation of bound residues is the adduct residue. The concept of adduct residue can be applied to any metabolite covalently linked to an endogenous component. Hydrolysis of Ure macromolecular bound residue, whether by enzymatic or chemical means, may lead to lower-molecular-weight adduct residues, free residues, and residue fragments. Since bound residues are derived from reactive metabolites, the reversibility of adduct formation to yield reactive compounds may be a key factor in the safety assessment of bound residues. 

Besides the peak current and the reversibility of the redox system and its current-potential curve, the inclining part of the forward wave has also been a target for extensive studies and characterisation. Numerous mathematical approaches have been presented in the literature however, the approach of Nicholson and Shain has been chosen here11 due to the clarity of the physical-chemical meaning behind the mathematical approach and the ease with which non-electrochemists can understand the shape of the voltammetric curve. In their approach, a current-potential curve of a reversible system is presented as ... 

Carbon dioxide removal by reactive absorption in amine solutions is also applied on the commercial scale, for instance, in the treatment of flue gas (see later in this chapter). Another possible application field of the technique is gas desulfurization, in which H2S is removed and converted to sulfur by means of reactive absorption. Aqueous solutions of ferric chelates (160-162) as well as tetramethylene sulfone, pyridine, quinoline, and polyglycol ether solutions of S02 (163,164) have been proposed as solvents. Reactive absorption can also be used for NOx reduction and removal from flue or exhaust gases (165,166). The separation of light olefins and paraffins by means of a reversible chemical com-plexation of olefins with Ag(I) or Cu(I) compounds in aqueous and nonaqueous solutions is another very interesting example of reactive absorption, one that could possibly replace the conventional cryogenic distillation technology (167). 

NaCl(s). What does it mean when there is a double arrow in a chemical equation Here is an equation with a double arrow A + B <—> C + D. Reactions with a double arrow mean that the reaction is a reversible reaction. As substances A and B react to form the products C and D (the forward reaction), the products C and D can form the original reactants (the reverse reaction). It sounds counterproductive, but it happens. Later you will see how conditions can be manipulated to make a reaction favor the products, but for now the focus is only on what a reversible reaction means for the enthalpy changes during the reaction. 

It will be shown in a forthcoming review that a reversible change of conformation of linear macromolecules in solution may result in an appredable change of solution properties, and particularly of their viscosity. Such conformational changes and the resulting effects can be displayed by chemical means, and were actually described several years ago by Kuhn, Katchalsky and coworkers " and more recently by Osada and Saito. They are responsible for the mechanochemical behavior of polymer systems in the solid state, i.e. the conversion of chemical into mechanical energy . ... 

In a third approach, supramolecular polymers are based on the reversibility of metal-coordination bonding. These polymers are the closest analogues to conventional macromolecules, because most of the polymers disclosed make use of strong bonding,16 in which the reversibility can be tuned by chemical means only. However, appropriate choice of the metal ion can give rise to bonding that resembles that of the other two approaches. The DP of the polymers in the case of the coordination polymers is similar to that of the condensation polymers, and achieving exact stoichiometry is of distinct importance here. 

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