Reactivity, dissolved constituents

The ratio of the inventory (total amormt) of an element in the sea to its inflow (or outflow) rate at steady state (rmchanging total mass) is a measme of its reactivity. These two terms combine to form the residence time of the dissolved constituent with respect to river inflow, tr ... 

The disappearance of a solvent fi om solution can also be the result of a number of abiotic and biotic processes that transform or degrade the compound into daughter compounds that may have different physicochemical properties from the parent solvent. Hydrolysis, a chemical reaction where an organic solvent reacts with water, is not one reaction, but a family of reactions that can be the most important processes that determine the fate of many organic compounds. Photodegradation is another family of chemical reactions where the solvent in solution may react directly under solar radiation, or with dissolved constituents that have been made reactive by solar radiation. For example, the photolysis of water yields a hydroxyl radical ... 

Photodegradation is another family of chemical reactions where the plasticizer may react directly with solar radiation or with dissolved constituents made reactive by solar radiation. Photodegradation may be an important fate mechanism in the atmosphere (see 18.5), but it is generally thought that plasticizers do not photodegrade significantly by either photolysis or photooxidation. 

Various fluorides may be precipitated from aqueous solution for use as constituent powders in solid state reactions. Co-precipitation offers very elegant access to intimate mixtures, but the actual products are strongly dependent on the fluoride ion activity within the solution but also on the stability constants of the respective metal complexes. Accordingly, not only anhydrous fluorides are obtained, but also hydrated fluorides or hydroxide fluorides, which may be very difficult to convert to pure fluorides. As noted already [3], reactive compounds, e.g. carbonates, acetates, oxalates, hydroxides etc., which quite easily dissolve in acidic HF solutions, are the preferred starting materials for fluoride syntheses. In contrast, many oxides which have been heated to rather high temperature are frequently unreactive and may not dissolve at all. To enhance reactivity but also improve crystallinity of the product, it has proved useful to perform reactions above the boiling point of water in adapting the hydrothermal method, which has already been shown to be useful in the recrystallisation of materials which are more or less insoluble at ambient temperatures and pressures. Up to about 240°C even PTFE vessels may be used. A number of selected examples with respective reaction conditions are listed in Table 3. 

If we mix water and alcohol (C2H5OH, ethanol), they dissolve to form a single liquid phase. The partial pressures of the individual vapours get reduced in this process compared to what they were, when the constituents were in pure state. The tendencies to react of both these constituents also goes down compared to the level of reactivity when they were in pure state. We say that the activities of the constituents decrease when they go into solution. 

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