Photochemical Reactions

It is a chemical reaction kicked off by the absorption of energy in the form of light. The results of molecules’ absorbing lights are the conception of transient energized states whose chemical physical properties distinguish greatly from the original molecules. The fresh chemical species can fall apart, transform to strange structures, mix with each other or other molecules, or transfer electrons, hydrogen atoms, protons, or their electronic excitation energy to other molecules. The energized states are sturdy acids and burly reductants than the actual ground states.

The process and occurrence

The final step is vital of all the photochemical processes, the photosynthesis over which most life on earth depends. The plants change the energy of sunlight into stored chemical energy by forming carbohydrates from atmospheric carbon dioxide and water and releasing molecular oxygen as a byproduct.  The both the elements like carbohydrates an oxygen are required to continue animal life. There are such processes in nature which are photochemical reaction.

The formation of photochemical reaction

The capacity to look around begins with a photochemical reaction in the eye, where retinal a molecule in the photoreceptor cell rhodopsin, isomerizes about a double bond after exposure of the chemical 7-dehydrocholestral to sunlight. The ozone protects earth’s surface from intense, deep ultraviolet radiation which damages the DNA and are formed in the stratosphere by a photochemical disassociation of molecular oxygen into oxygen atoms, followed by a subsequent reaction of those oxygen atoms with molecular oxygen to produce ozone.  UV radiation that gets through the ozone layer photochemiclly damages DNA, which in turn introduces mutations on its replication that can lead to skin cancer.

Photochemical reaction and the properties of excited states are also critical in many commercial processes and devices. Photography and xerography are both upon photochemical processes, while the manufacture of semiconductor chips or the preparation of masks for printing newspapers relies on UV light to destroy molecule in selected regions of polymer masks.

Principles and earlier times

Research shows that human beings have started to use photochemistry since 1500 BC revolving around the Bronze Age. In an ordinary photochemical process, excited states can emit light in the form of fluorescence of phosphorescence.

Light is one of the electromagnetic radiations, which are a source of energy. The Grotthuss-Draper law explains that light must be absorbed by a chemical substance in order for a photochemical reaction to occur.  Every time photon of light is absorbed by a chemical system, one molecule is activated for a photochemical reaction and not more, as according to the quantum yield.

Questions:

• What is photochemical reaction?
• State the importance of photochemical reaction in chemical engineering.