Sky Of Chemistry

A photochemical reaction involves two processes. One is the  primary process in which light is absorbed by molecules to give excited molecules. Another is a  secondary process in this process exciting molecule initiates a series of thermal reactions. In such reactions, many reactant molecules may undergo chemical change by absorbing one quantum only. In some cases, the activated molecule undergoes deactivation. Thus, less than one molecule may react per quantum. The overall result of the photochemical reaction is expressed in terms of Quantum yield.  The quantum yield or efficiency(Φ) is defined as: " It is the number of molecules which undergo chemical transformation per quantum of absorbed energy. " Mathematically, Φ = No. of molecules reacting in a given time/ No. of quanta absorbed in the same time Φ = No. of moles reacting in a given time/ No. of Einsteins absorbed in the same time Φ = Rate of chemical reaction/ No. of Einsteins absorbed  The quantum yields are depende

Laws of Photochemistry (1) Grotthuss-Draper law (First Law of Photo-chemistry): Only the light which is absorbed by a molecule can be effective in producing photochemical changes in the molecule. "When light y on any substance, only the fraction of incident light which is absorbed by the substance can bring about a chemical change, reflected and transmitted light do not produce any such effect." This law is purely qualitative. It doesn't give any relationship between the amount of light absorbed by a system and the number of molecules reacted. (2) Stark-Einstein's Law (Second Law of Photo-chemistry): "It states that for each photon of light absorbed by a chemical system, only one molecule is activated for a photochemical reaction." Einstein applied quantum theory to photochemical reactions and gave the law. " When an atom or molecule absorbs light of a given frequency, it absorbs one quantum only" The energy absorbed by one mole of the reacting mol

When light is incident upon a homogeneous medium, a part of the incident light is reflected, a part is absorbed and the rest is transmitted. I 0 = I a + I t + I r                                                                        ...........................(1) Where, I 0 = Incident light             I a = Absorbed light             I t = Transmitted light             I r = Reflected light. Ir is very small, so eq.(1) becomes, I 0 = I a + I t                                                                    ......................(2) Lambert's law:  " When a beam of light is allowed to pass through a transparent medium, the rate of decrease of intensity with the thickness of medium is directly proportional to the intensity of the light."  "This law states that decrease in the intensity of monochromatic light with the thickness of the absorbing medium is proportional to the intensity of incident light." -dI/dx ∞ I      or     -dI/dx = KI,             

Thermochemical(Dark) Reactions Photochemical Reactions (1) It involves absorption or evolution of heat. (1) It involves absorption of light. (2) It can occur in dark as well as in light. (2) Presence of light is a must. (3) Temperature has a significant effect on the rate of reaction. (3) Temperature has very little effect on the rate of reaction. (4) These reactions are always accompanied by a decrease in free energy. In these reactions,   free energy may increase or decrease. (5) Activation energy is obtained by intermolecular collisions. (5) Activation energy is obtained by a particular type of radiation. (6) Thermal excitation increases in a random manner. i.e. translational, rotational and vibrational energy of all the molecules increases. (6) By selecting a particular type of radiation particular atom or mol

Introduction Photochemistry is the study of chemical effects produced by light radiations ranging from 2000 to 8000 Å wavelength. Type of Chemical Reaction: A chemical reaction is one in which, the identity of molecules is changed due to the breaking and formation of chemical bonds. There are two types of chemical reactions. (i) Dark or Thermal reaction: The reaction which is influenced by temperature, the concentration of reactants, catalyst etc. except light radiations are known as thermal reactions. N 2 + 3H 2 ⇌ 2NH 3 H 2 + I 2     ⇌ 2HI (ii)Photochemical Reactions: The reaction which is influenced by the action of light is known as photochemical reactions.  Some examples are following, 2HBr ⟶ H 2 Follow us on Social media for the latest information about the blog.👇👇

Introduction Proteins are very big molecules made up of smaller units known as 'Amino Acids'. Amino acids are organic molecules that contain an amino group and a carboxylic acid group. all amino acids have a simple chemical backbone with an amine group (the nitrogen-containing part) at one end. At the other end is the acid part. This backbone is the same for all amino acids. The difference between them depends on a distinctive structure, the chemical side chain that is attached to the backbone. It is the nature of the side chain that gives identity and chemical nature to each amino acid. There are about 20 different naturally occurring amino acids that combine to from proteins of all living tissue. The amino acids that make up proteins differ from fats and carbohydrates in that they contain the element nitrogen. The amino acids in proteins are called alpha (α)-amino acids because the amino group is attached to the α-carbon connected to any carboxylic acid carbon is termed a