Drive, chemical

Reducing the intrinsic hazard of chemicals is the most effective and most fundamental of the risk reduction options available. Intrinsic risk reduction is based on the principle that the structure of a chemical drives hazard and molecular intentional, informed manipulation will result in the design of safer chemicals. Wastewater treatment plants employ large filters packed with granular activated carbon to remove polluted water. Synthetic chemists are... 

The phenomena of cations being attracted to surfaces is commonly referred to as cation exchange because cations that are more attracted to the surface can displace those that are less attracted. For example, a +2 cation can displace a +1 cation from a surface because the +2 cation has a greater chemical drive to interact with a negatively charged surface than does the +1 ion. Thus, the +1 ion is exchanged for the +2 ion. 

Solution. Important assumptions include that the interfacial free energy is isotropic, that elastic strain energy is unimportant, and that the nucleation rates mentioned are for steady-state nucleation. The critical barrier to nucleation, AQe, can be calculated for the 0.3 atomic fraction B alloy using the tangent-to-curve construction on the curves in Fig. 19.18b to provide the value Aga = —9 x 107 Jm-3 for the chemical driving force for this supersaturation at 800 K. AQc is given for a spherical critical nucleus by... 

It means that when the chemical driving force (AG) is exactly balanced by the external opposing voltage (-E), the whole system (die cell) is at equilibrium, i.e., electrochemical equilibrium. 

Availability of Internal Surfaces to Dve Molecules. Absorption of cationic dyes by dilute suspension is an interesting tool for obtaining information on the availability of the clay surface. Dyes such as methylene blue, safranine, etc. undergo protonation and molecular association within the interlamellar space. Both these chemical driving forces may overcome the cohesion forces between clay sheets. Table 1 shows the results of the analysis of the... 

These remarks must be balanced by some characteristic difficulties of using the electrochemical path. Sometimes, and in spite of tight potential control, two or more reactions take place at the same time and give not one product but a mixture. Correspondingly, overoxidation may occur the intended oxidation may continue to a further step by means of a chemical driving force outside the control of the potentiostat. 

Combining chemical reaction and separation in a reactive-distillation device, can lead to significant economic advantage in term of investment and operation costs. Because the chemical driving force can be lowered by vapor-liquid equilibrium, this should be compensated by a more active catalyst. 

The chemical driving force on a stage has inlet and outlet concentrations as boundary conditions. In the enriching section below the feed plate, a flowfrom liquid to vapor occurs while in the stripping section, the direction of flow is from vapor to liquid. For the column with specified inlet and outlet compositions, the entropy production rates are... 

This contribution deals with thermodynamics and kinetics of charge carriers in solids in the case of zero or non-zero electrical or chemical driving forces. It does not intend to repeat well-known electrochemical principles, however, it intends to underline the special situation in solids by, on one hand, emphasizing characteristic aspects due to the solid nature, but on the other hand, stressing the common and generalizing aspects of the picture whenever it appears necessary. This also implies that specific solid state aspects (such as structural details, anisotropies or strain effects) are neglected whenever their influence is not indispensable for the understanding. 

The three experiments do not only introduce decisive mass and charge transport parameters, they also permit their determination. Some points relevant in this context will be investigated in the following. (Note that electrochemical measurement techniques are covered by Part II.1) At the end of this section we will have seen that—close to equilibrium—not only all the D s and the k s can be expressed as the inverse of a product of generalized resistances and capacitances, but that these elements can be implemented into a generalized equivalent circuit with the help of which one can study the response of a material on electrical and/or chemical driving forces. 

In the framework of linear irreversible thermodynamics it is possible to handle responses to electrical and/or chemical driving forces, as could be seen from the previous sections, by what is called Nernst-Planck-... 

A dead battery is one in which the cell reaction has reached equilibrium there is no longer any chemical driving force to push electrons through the wire. In other words, at equilibrium the components in the two cell compartments have the same free energy that is, AG = 0 for the cell reaction at the equilibrium concentrations. The cell no longer has the ability to do work. 

Similarly, the work done against an opposing force by a system undergoing a chemical change is proportional to the amount of substance transformed by the reaction. The maximum work done in the transformation of unit mass—one equivalent of each substance—can only be expressed in terms of the opposing force when the chemical driving force and the external opposing force are equal to one another. Van t Hoff took the work obtainable in the transformation of unit mass as a measure of the chemical affinity. This definition of the affinity as an amount of work done enables us to measure affinity in terms of mechanical, electrical, and thermal quantities. 

TABLE 1. Coupling among Macroscopic Transport Processes and Physical, Hydrological, and Chemical Driving Forces... 

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