Photochemical reactions involve a variety of chemical processes that are catalyzed by light. In general, light acts as a trigger to begin the reaction, with the photon energy causing the reactants to break apart and form products. In this article, we will examine the definition and overview of photochemical reactions, explore the components and key characteristics of these reactions, and discuss their applications in everyday life.
Photochemical reactions are chemical reactions initiated by absorbing energy from light. This energy is commonly in the form of ultraviolet radiation, and can be absorbed by specific compounds called chromophores, which then absorb and convert the energy into chemical energy and cause the reaction. Photochemical reactions can be either photodecomposition or photoreduction reactions.
In photodecomposition reactions, the photochemical reaction results in the breaking of molecular bonds, leading to the formation of several separate products from the original molecule. A classic example is photosynthesis, where the absorption of light energy leads to the hydrolysis of water molecules and the formation of oxygen and glucose molecules.
In photoreduction reactions, the photochemical reaction results in the formation of new bonds in the molecules, leading to the formation of a single product from the original molecules. An example of this is the photo-reduction of carbon dioxide to form formaldehyde. In these reactions, light energy acts as an electron donor in the form of photons, and these electrons break the existing bonds, leading to the formation of new molecules.
Photochemical reactions involve the absorption of light energy by a molecule, resulting in changes in the molecular structure. In order for photochemical reactions to occur, certain components are necessary. These components include a compound that is capable of absorbing light energy, usually referred to as a chromophore, and at least one other active species known as the photosensitizer. Together, these components form a photo-reaction complex which facilitates the transfer of energy from the chromophore to the photosensitizer.
Illustrative examples of photochemical reactions include those involving the oxidation of certain organic substances by oxygen when exposed to sunlight. This can occur in the presence of compounds like benzophenone or anthraquinone, which act as chromophores in the reaction. The photosensitizers in this case can range from halogens, aldehydes, ketones and hydrocarbons, allowing for a wide range of chemical transformations. In some cases, even a catalyst can be employed to accelerate the reaction.
Another familiar example is that of photosynthesis, the key biological process used by plants to convert sunlight into usable energy. The chromophore in this case is chlorophyll, while the photosensitizer is an enzyme called RuBisCO. This reaction is highly exothermic and involves the breakdown of water molecules, followed by the release of oxygen into the atmosphere.
Photochemical reactions have many applications in everyday life. One of the most notable is photosynthesis, which plants use to convert light energy into chemical energy. Photosynthesis is necessary for the survival of all plants and is a key component of the food web. In addition, these photochemical reactions can be used to generate electricity, such as through solar cells. Photovoltaic cells are a type of solar cell that absorbs light particles and converts them into electrical current. This electricity can then be used to power homes and businesses. Finally, photochemical reactions are also used to create medical treatments, such as photodynamic therapy. In this therapy, specific cells are exposed to light which causes them to react and produce new compounds that can help treat diseases and disorders. Ultimately, applications of photochemical reactions in everyday life are numerous, making them an important and versatile tool.