Physical Chemistry
Physical chemistry is the branch of chemistry which deals with the physical foundations of chemical substances and processes. Thus, for example, physicial chemists strive to understand the physical mechanisms underlying chemical reactions. It us important to note that research in physical chemistry depends on the development of new techniques and instruments.
Physical chemistry is generally divided into a variety of branches, including chemical physics (the study of the chemical propereties of atoms and molecules) and theoretical chemistry (the mathematical interpretation of quantum and thermodynamic processes).
Essentially, the physical chemist studies matter—its changes, structure, and chemical equilibrium.
Matter can undergo two types of changes, chemical and physical. A chemical change occurs when a substance reacts chemically to form a new substance. An example of this kind of change is combustion. Thus, when wood, a compound composed of mainly carbon (C), hydrogen (H), and oxygen (O), burns, it changes to ashes, consisting mostly of carbon, water, and carbon dioxide.
An example of a physical changes would be chopping a piece wood into smaller pieces or melting ice. The physical chemist is concerned concerned with the rate of change in a substance, which is the study of reaction kinetics. Diffusion and ionization are both examples of physical changes which would be studied by a physical chemist. The diffusion of gases, for example, is usually described in terms of kinetic energy of the gas particles. The physical chemist would study the molecular forces between the particles (a transport process), not the kinetic energy of the particles. Inoization concerns the movement of ions in a solution, which is also a transport process. The study of transport processes in physical chemistry is done by scientists who specialize in non-equilibrium dynamics.
Physical chemists explore many types of chemical change. The rate of chemical reactions often depends on the concentration of the reactants involved. Reaction rate can also be affected by conditions such as temperature, agitation of the reaction mixture, or addition of catalysts. Scientists working in physical chemistry have formulated several laws which can be used to predict the rate of chemical reaction, including the rate coefficient (which explains how the cocentrations of the reactants affect the rate) and the Arrhenius rate law (which describes the role of temperature in reaction kinetics).
The study of chemical kinetics is either based on the statistical model of thermodynamics or the calculated trajectories of the molecules involved in a reaction. The statistical model of thermodynamics is called the activated complex theory, and is the main tenet of the field of molecular reaction dynamics. The calculation of trajectories is called the particle dynamics approach. Physical chemists involved in particle dynamics calculate the paths of a molecule and converts these into rate coefficients. Historically, these methods of determining the chemical kinetics of a reaction has been primarily theoretical. Experimental methods are now being developed which allow scientists to actually observe the molecules involved in a chemical reaction--metods such as "molecular beams." During a chemical reaction, a beam of one reactant is directed at a beam of the other reactant. Scattering of the products is observed to determine the trajectories of the molecules involed. This technique enables scientists to get an accurate description of the chemical kinetics for many types of reactions.
Physical chemist study the structure of matter by using several innovative techniques. The study of molecular and atomic structure is called quantum chemistry, or quantum mechanics. For example, the structure of many atoms and molecules can be predicted by solving the Schrödinger's equstion. The numerical solution of this equation allows scientists to determine the wave functiond and geometries of molecules. Other equation shave been developed to predict the shape and electron distribution of molecules. These equations are so advanced that they can be use dto determine the charges in structure of a molecule during each phase of a reaction
The shape, size, and electron distribution of molecules can also be determined by using spectroscopy. For categories of spectroscopic techniques used by physical chemists are absorption spectroscopy, emission spectroscopy, Raman spectroscopy, and resonance techniques. The size and shape of a molecule can be determined by using absorption spectroscopy. In this this procedure, the amount of radiation emitted by a molecule is observed at different wavelengths. The frequency of light emitted from atoms in an excited state is measured in emission spectroscopy. These data allow scientists to identify molecules, as well as the processes whjich occur during a reaction. Light emitted from molecules is measured n Raman spectrometry, which is used, in combination with other forms of spectrometry, to provide additional information. Resonance techniques are used to measure the frtequencies of excited molecules in resonance with surrounding radiation. These techniques, which include nuclear magnetic resonance (NMR), electron spin resonance (ESR), and Mossbauer spectroscopy, provide vaaluable information about the structure of a molecule.
Physical chemists use other techniques to determine the structure of atoms and molecules as well. For example, diffraction techniques involve directing radiation toward a sample and observing the direction of the resulting scatter. An example of a diffraction technique is x-ray diffraction, which provides detailed information aout the atoms in crystals or large biological molecules. Electrical properties such as dipole moments, magnetic properties, optical properties, and the Faraday effect all give important information about the structure of molecules as well.
Matter in the state of equilibrium is studied by physical chemists specializing in chemical thermodynamics and equilibrium electrochemistry. Chemical thermodynamics is concerned with the response of a reaction system to changes in external variables such as pressure, temperature, or composition of the reaction mixture. Thermochemistry is a branch of chemical thermodynamics, which is the study of the energy involved in a chemical reaction. The energy involved in a reaction is directly related to its efficiency. Physicial chemists specializing in thermodynamics caan apply their research findings to improve the efficiency of such devices as as batteries, engines, and refrigerators. Scientists can also use the thermodynamics of a reaction to determine how to increase thge yield of a chemical reaction for industrial purposes.
The laws of thermodynamics are valuable tools for the physical chemist. For example, the change in enthalpy can be used to predict the heat involved in a particular reaction. The heat involved in a reaction is an indication of the energy involved, and therfore an indication of the efficiency of a reaction. Gibbs free energy is another important thermodynamic property. The Gibbs free energy of as reaction describes the amount of work done in the reaction, and this information can be used to explain complicated processes such as those involved in biological growth.
Equilibrium electrochemistry studies the behavior of chemical reactions which release energy in the form of electron flow. This branch of physical chemistry determines the equilibria of ionic reactions and their response to changes in external variables. Applications of equilibrium electrochemistry include the analysis of electrochemical cells, fuel cells, and the power of batteries,
Physical chemistry is an important branch of chemistry which studies the processes involved in chemical reactions. Chemical kinetics, the structure of atoms and molecules, and the equilibria of chemical reactions are studied by the physical chemist. The methods involved in physical chemistry are extremely complicated and quite advanced. Physical chemists use a wide variety of techniques and procedures in their research. Physical chemistry provides the basis for all other branches of chemistry by explaining the fundamental processes involved in the formation of chemical substances. A growing, vitally important field, this branch of chemistry is also important for determining the efficiency and productivity of technologies developed by other chemists.
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