First Law of Photochemistry

This principle is so simple that it has been given the title the first law of photochemistry, and was first expressed by Grotthus and Draper in the early 19th century. They stated it as the (hopefully) obvious truth Only light that is absorbed can have any photochemical effect . 

The first law of photochemistry states that only light that is absorbed can have any photochemical effect. 

The so-called first law of photochemistry stating that only the radiation absorbed by a molecular entity or substance is effective in producing a photochemical change. 

The first law of photochemistry states Only that light which is absorbed by a system can cause chemipal change (Grotthus-Draper Law). 

The Grotthus-Draper law states that photophysical/photochemical reactions occur only when a photon of light is absorbed. This forms the basis for the First Law of Photochemistry—that is, only light that is absorbed can have a photophysical/photochemical effect. 

The first law of photochemistry states that a molecule must first absorb light in order to undergo a photochemical transformation. This law in embodied in the Beer-Lambert law... 

The first law of photochemistry, named the Grotthus-Drapper Principle, states that for a photochemical reaction to occur, the first event must be the absorption of light by some component of the system. The second law of photochemistry, named the Stark-Einstein Principle, states that a molecule can only absorb one quantum of radiation. The absorbed energy in the resultant excited molecule may be dissipated by either photophysical or photochemical processes. It is the latter of these that eventually changes the chemical and mechanical properties of the substance (26,27). Thus, the reactions based on the absorption of radiation by the chemical components of modern papers are of prime importance in discoloration. 

The first law of photochemistry, called the Grottus Draper law, states Only the light, which is absorbed by a molecule, can be effective in producing photochemical changes in the molecule. 

Although the first law of photochemistry had already been recognized by Grot-thus in 1817 and Draper in 1843, the quantum nature of UV/VIS radiation and their consequences for photochemistry were established only decades later by Planck and Einstein (see Tab. 2-2). Nowadays, the observation by Grotthus and Draper that only electromagnetic radiation that is absorbed by a molecule leads to a... 

The effects of mixing on photochemical reactions are not well known. As a corollary of the first law of photochemistry (see Chapters 6 and 8), primary photochemical reaction rates should be directly proportional to the rate of light absorption. However, the previous statement applies only to completely mixed, optically thin water bodies, or where the reactant is the sole absorber [39]. In contrast, in optically thick water columns with competition amongst chromo-phores for photons, differences in mixing rates can affect photochemical reaction rates. Under such circumstances, fast turnover would tend to release the CDOM pool from self-shading, which should translate into higher photoreaction rates [40]. 

The first law of photochemistry (Grothus, 1817 Draper, 1843) states that only absorbed light is effective in photochemical transformation. 

The first law of photochemistry states that "in order for photochemistry to occur, radiation must be absorbed." A useful corollary to this law for UV curing is that the only wavelengths which need be considered are those emitted by the radiation source. For the data in Table I we have used this corollary to... 

When a molecule or ion absorbs a photon, that photon s energy can be dissipated in several different ways, but one way is for that energy to cause a chemical reaction to occur. The first law of photochemistry is that a compound must absorb light for a photochemical reaction to occur (Grotthuss-Draper law). The second law of photochemistry is that each photon that is absorbed activates only one molecule for a subsequent reaction (Stark-Einstein law). The quantum yield ( ) is defined as the number of molecules that react divided by the number of photons absorbed. It can also be defined in terms of moles. 

The photochemical reaction of a material starts with photon absorption. In other words, only the photons absorbed by the molecule can bring about photochemical reactions. This is the first law of photochemistry, also called the Grotthuss-Draper law. The second law of photochemistry is one molecule is activated when one photon is absorbed. This is called the Stark-Einstein photochemical equivalence law. Generally, a particular group in an irradiated molecule absorbs a photon with an appropriate wavelength. When photoabsorption occurs, the molecule in the ground state is... 

He concluded that the situation may be met by means of two laws of photochemistry. The first law of photochemistry would be the Grotthuss-Draper absorption law, embodied in the statement that ... 

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