photochemical equivalence law
- photochemical equivalence law
-
fundamental principle relating to chemical reactions (
chemical reaction) induced by
light, which states that for every
quantum of
radiation that is absorbed, one
molecule of the substance reacts. A quantum is a unit of
electromagnetic radiation with energy equal to the product of a constant ( Planck's constant,
h) and the frequency of the radiation, symbolized by the Greek letter nu (ν). In chemistry, the quantitative measure of substances is expressed in terms of gram moles (
mole), one gram mole comprising 6.02214179 × 10
23 ( Avogadro's number) molecules. Thus, the photochemical equivalence law is restated as: for every mole of a substance that reacts 6.02214179 × 10
23 quanta of light are absorbed.
The photochemical equivalence law applies to the part of a light-induced reaction that is referred to as the primary process; that is, the initial chemical change that results directly from the absorption of light. In most photochemical reactions (
photochemical reaction) the primary process is usually followed by so-called secondary processes that are normal interactions between reactants not requiring absorption of light. As a result such reactions do not appear to obey the one quantum–one molecule reactant relationship. The law is further restricted to conventional photochemical processes using light sources with moderate intensities; high-intensity light sources such as those used in flash
photolysis and in
laser experiments are known to cause so-called biphotonic processes;
i.e., the absorption by a molecule of a substance of two photons (
photon) of light.
The photochemical equivalence law is also sometimes called the Stark–Einstein law after the German-born physicists Johannes Stark (
Stark, Johannes) and Albert Einstein (
Einstein, Albert), who independently formulated the law between 1908 and 1913.
* * *
Universalium.
2010.
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einstein law of photochemical equivalence — Usage: usually capitalized 1st E Etymology: after Albert Einstein : a law in quantum theory: each molecule activated in any photochemical process absorbs one photon of radiant energy compare einstein 1 … Useful english dictionary
Stark-Einstein law — The Stark–Einstein law is named after the German born physicists Johannes Stark and Albert Einstein, who independently formulated the law between 1908 and 1913. It is known also as the photochemical equivalence law or photoequivalence law. It… … Wikipedia
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Einsteinsches Gesetz — Einšteino fotochemijos dėsnis statusas T sritis fizika atitikmenys: angl. Einstein law of photochemical equivalence vok. Einsteinsches Gesetz, n; Äquivalentgesetz, n rus. фотохимический закон Эйнштейна, m pranc. loi d’Einstein sur l’équivalence… … Fizikos terminų žodynas
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