Urgente!!!!!!!!Costante di quenching???

Question

Sapete dirmi che unità di misura ha la costante dell'equazione di stern-volmer, se ce l'ha???

...ste cose già le sapevo...solo non mi capacito sull'unità di misura....sta k c'avrà un'unità....e se non ce l'ha che me lo dicano no???....sing ;(

Answer 1

atkins nn delude mai.... ^_^

sull'atkins chimica fisica nn la trovi come l'hai chiamata tu,ma come costante cinetica di estinzione ed è 2.8 * 10^9 L* mol^-1*s^-1

Answer 2

grande copia e incolla di alice!!!

Answer 3

Quench
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For other uses, see Quenching (disambiguation)

A quench refers to a rapid cooling. In polymer chemistry and materials science, quenching is used to prevent low-temperature processes such as phase transformations from occurring by only providing a narrow window of time in which the reaction is both thermodynamically favorable and kinetically accessible. For instance, it can reduce crystallinity and thereby increase toughness of both alloys and plastics (produced through polymerization).

In metallurgy, it is most commonly used to harden steel by introducing martensite, in which case the steel must be rapidly cooled through its eutectoid point, the temperature at which austenite becomes unstable. In steel alloyed with metals such as nickel and manganese, the eutectoid temperature becomes much lower, but the kinetic barriers to phase transformation remain the same. This allows quenching to start at a lower temperature, making the process much easier. High-speed steel also has added tungsten, which serves to raise kinetic barriers and give the illusion that the material has been cooled more rapidly than it really has. Even cooling such alloys slowly in air has most of the desired effects of quenching.

In fluorescence, it refers to any process which decreases the fluorescence intensity of a given substance. A variety of processes can result in quenching, such as excited state reactions, energy transfer, complex formation and colissional quenching.

Molecular oxygen and the iodide ion are common chemical quenchers.

In superconducting magnet technology, quench refers to a thermal runaway of the superconducing magnet. The energy stored in the magnet is released leading to an increase in the magnet's temperature.

In a high voltage spark gap, fuse, or circuit breaker, quenching refers to the successful extinguishing an electric arc. Quenching is accomplished by temporarily removing current (possibly during an AC zero crossing, or by physically stretching or rapidly cooling the arc's channel). Once quenched, the dielectric strength of the gap recovers sufficiently to prevent immediate reignition of the arc.

[edit] Role of quenching in scrubbing

Occasionally, hot exhaust gas is quenched or cooled by water sprays before entering the scrubber. Hot gases (those above ambient temperature) are often cooled to near the saturation level.

If not cooled, the hot gas stream can evaporate a large portion of the scrubbing liquor, adversely affecting collection efficiency and damaging scrubber internal parts. If the gases entering the scrubber are too hot, some liquid droplets may evaporate before they have a chance to contact pollutants in the exhaust stream, and others may evaporate after contact, causing captured particles to become reentrained. In some cases, quenching can actually save money.

Cooling the gases reduces the temperature and, therefore, the volume of gases,permitting the use of less expensive construction materials and a smaller scrubber vessel and fan.

A quenching system can be as simple as spraying liquid into the duct just preceding the main scrubbing vessel, or it can be a separate chamber (or tower) with its own spray system identical to a spray tower.

Quenchers are designed using the same principles as scrubbers. Increasing the gas-liquid contact in them increases their operational efficiency. Small liquid droplets cool the exhaust stream more quickly than large droplets because they evaporate more easily. Therefore, less liquid is required. However, in most scrubbing systems, approximately one-and-a-half to two and- a-half times the theoretical evaporation demand is required to ensure proper cooling (Industrial Gas Cleaning Institute 1975). Evaporation also depends on time - it does not occur instantaneously.

Therefore, the quencher should be sized to allow for an adequate exhaust stream residence time. Normal residence times range from 0.15 to 0.25 seconds for gases under 540°C (1000°F) to 0.2 to 0.3 seconds for gases hotter than 540°C (Schifftner 1979).

Quenching with recirculated scrubber liquor could potentially reduce overall scrubber performance, since recycled liquid usually contains a high level of suspended and dissolved solids. As the liquid droplets evaporate, these solids could become reentrained in the exhaust gas stream. To help reduce this problem, clean makeup water can be added directly to the quench system rather than adding all makeup water to a common sump. [1]

[edit] External links

* J.L. Becker Company - Manufacturer of quenching and other heat treating systems & components

[edit] References

1. ^ *US EPA Air Pollution Training Institute developed in collaboration with North Carolina State University, College of Engineering (NCSU)



il quenching è un raffreddamento brusco di un prodotto petrolifero tramite iniezione di un fluido a temperatura più bassa. Nel reforming termico all'uscita del forno, si opera il quenching e contemporaneamente una rapida espansione, per diminuire la temperatura della carica per bloccare le reazioni di reforming.

Ho sopra riportato un brano dalla Wikipedia, nel quale ci sono vari riferimenti, per trovare qusta benedetta costante.

Intanto ti mando questo. Se trovo la costante, te la segnalerò.