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Activated Complex
In chemistry, an activated complex represents a collection of intermediate structures in a chemical reaction when bonds are breaking and forming. The activated complex is an arrangement of atoms in an arbitrary region near the saddle point In mathematics, a saddle point or minimax point is a Point (geometry), point on the surface (mathematics), surface of the graph of a function where the slopes (derivatives) in orthogonal directions are all zero (a Critical point (mathematics), ... of a potential energy surface. The region represents not one defined state, but a range of unstable configurations that a collection of atoms pass through between the reactants and Product (chemistry), products of a reaction. Activated complexes have partial reactant and product character, which can significantly impact their behaviour in chemical reactions. The terms activated complex and transition state are often used interchangeably, but they represent different concepts. Transition state ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ac Com
AC, A.C., A/C, or Ac often refers to: * Air conditioning, often abbreviated as A/C * Alternating current, a type of electrical current in which the current repeatedly changes direction AC, A.C. or Ac may also refer to: Arts and entertainment Gaming * '' Ace Combat'', a series of combat flight simulator games * ''Animal Crossing'', a series of community simulation games * '' Anonymous;Code'', a visual novel in the Science Adventure series * '' Another Code'', a series of adventure games * '' Armored Core'', a series of mecha-based third person shooter games * '' Asheron's Call'', a fantasy massively multiplayer online role-playing game * ''Assassin's Creed'', a series of action-adventure games * '' Assetto Corsa'', a racing simulator game * '' Astral Chain'', an action-adventure hack and slash game * Armor Class, a combat-related parameter in the ''Dungeons & Dragons'' role playing game system * A.C., a character in '' Fortnite: Save the World'' Music * A.C. Newman, solo stag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Activation Energy
In the Arrhenius model of reaction rates, activation energy is the minimum amount of energy that must be available to reactants for a chemical reaction to occur. The activation energy (''E''a) of a reaction is measured in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol). Activation energy can be thought of as a magnitude of the potential barrier (sometimes called the energy barrier) separating minima of the potential energy surface pertaining to the initial and final thermodynamic state. For a chemical reaction to proceed at a reasonable rate, the temperature of the system should be high enough such that there exists an appreciable number of molecules with translational energy equal to or greater than the activation energy. The term "activation energy" was introduced in 1889 by the Swedish scientist Svante Arrhenius. Other uses Although less commonly used, activation energy also applies to nuclear reactions and various other physical phenomena. Temperature ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Symmetry Number
The symmetry number or symmetry order of an object is the number of different but indistinguishable (or equivalent) arrangements (or views) of the object, that is, it is the order of its symmetry group. The object can be a molecule, crystal lattice, lattice, tiling, or in general any kind of mathematical object that admits symmetries. In statistical thermodynamics, the symmetry number corrects for any overcounting of equivalent molecular conformations in the partition function. In this sense, the symmetry number depends upon how the partition function is formulated. For example, if one writes the partition function of ethane so that the integral includes full rotation of a methyl, then the 3-fold rotational symmetry of the methyl group contributes a factor of 3 to the symmetry number; but if one writes the partition function so that the integral includes only one rotational energy well of the methyl, then the methyl rotation does not contribute to the symmetry number. Symmetry ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Annual Review Of Physical Chemistry
''Annual Review of Physical Chemistry'' is a peer-reviewed scientific journal published by Annual Reviews. It covers all topics pertaining to physical chemistry. The editors are Todd J. Martínez (Stanford University) and Anne McCoy (University of Washington). As of 2023, ''Annual Review of Physical Chemistry'' is being published as open access, under the Subscribe to Open model. The journal is indexed in the Science Citation Index Expanded and Chemical Abstracts Service. As of 2024, ''Journal Citation Reports'' gives it a 2023 impact factor of 11.7. History The ''Annual Review of Physical Chemistry'' published its first volume in 1950. Its founding editor was University of California chemist Gerhard Krohn Rollefson. Some branches of physical chemistry were designated to be reviewed with each volume, while other branches would be reviewed less frequently. Upon Rollefson's death in 1955, he was succeeded by Henry Eyring. The editorial committee considered changing the name o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Classical Mechanics
Classical mechanics is a Theoretical physics, physical theory describing the motion of objects such as projectiles, parts of Machine (mechanical), machinery, spacecraft, planets, stars, and galaxies. The development of classical mechanics involved Scientific Revolution, substantial change in the methods and philosophy of physics. The qualifier ''classical'' distinguishes this type of mechanics from physics developed after the History of physics#20th century: birth of modern physics, revolutions in physics of the early 20th century, all of which revealed limitations in classical mechanics. The earliest formulation of classical mechanics is often referred to as Newtonian mechanics. It consists of the physical concepts based on the 17th century foundational works of Sir Isaac Newton, and the mathematical methods invented by Newton, Gottfried Wilhelm Leibniz, Leonhard Euler and others to describe the motion of Physical body, bodies under the influence of forces. Later, methods bas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planck Constant
The Planck constant, or Planck's constant, denoted by h, is a fundamental physical constant of foundational importance in quantum mechanics: a photon's energy is equal to its frequency multiplied by the Planck constant, and the wavelength of a matter wave equals the Planck constant divided by the associated particle momentum. The constant was postulated by Max Planck in 1900 as a proportionality constant needed to explain experimental black-body radiation. Planck later referred to the constant as the "quantum of Action (physics), action". In 1905, Albert Einstein associated the "quantum" or minimal element of the energy to the electromagnetic wave itself. Max Planck received the 1918 Nobel Prize in Physics "in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta". In metrology, the Planck constant is used, together with other constants, to define the kilogram, the SI unit of mass. The SI units are defined in such a way that, w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermodynamic Temperature
Thermodynamic temperature, also known as absolute temperature, is a physical quantity which measures temperature starting from absolute zero, the point at which particles have minimal thermal motion. Thermodynamic temperature is typically expressed using the Kelvin scale, where the unit of measurement is the ''kelvin'' (unit symbol: K). The Kelvin scale uses the same degree interval as the Celsius scale but is offset so that 0 K corresponds to absolute zero. For comparison, a temperature of 295 K corresponds to 21.85 °C and 71.33 °F. Another absolute scale of temperature is the Rankine scale, which is based on the Fahrenheit degree interval. Historically, thermodynamic temperature was defined by Lord Kelvin in terms of a macroscopic relation between Work (thermodynamics), thermodynamic work and Heat, heat transfer as defined in thermodynamics, but the kelvin was redefined by international agreement in 2019 in terms of phenomena that are now understood as man ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boltzmann Constant
The Boltzmann constant ( or ) is the proportionality factor that relates the average relative thermal energy of particles in a ideal gas, gas with the thermodynamic temperature of the gas. It occurs in the definitions of the kelvin (K) and the molar gas constant, in Planck's law of black-body radiation and Boltzmann's entropy formula, and is used in calculating Johnson–Nyquist noise, thermal noise in resistors. The Boltzmann constant has Dimensional analysis, dimensions of energy divided by temperature, the same as entropy and heat capacity. It is named after the Austrian scientist Ludwig Boltzmann. As part of the 2019 revision of the SI, the Boltzmann constant is one of the seven "Physical constant, defining constants" that have been defined so as to have exact finite decimal values in SI units. They are used in various combinations to define the seven SI base units. The Boltzmann constant is defined to be exactly joules per kelvin, with the effect of defining the SI unit ke ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equilibrium Constant
The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency towards further change. For a given set of reaction conditions, the equilibrium constant is independent of the initial analytical concentrations of the reactant and product species in the mixture. Thus, given the initial composition of a system, known equilibrium constant values can be used to determine the Chemical equilibrium#Composition of a mixture, composition of the system at equilibrium. However, reaction parameters like temperature, solvent, and ionic strength may all influence the value of the equilibrium constant. A knowledge of equilibrium constants is essential for the understanding of many chemical systems, as well as the biochemical processes such as oxygen transport by hemoglobin in blood and acid–base homeostasis in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Collision Theory
Collision theory is a principle of chemistry used to predict the rates of chemical reactions. It states that when suitable particles of the Reagent, reactant hit each other with the correct orientation, only a certain amount of collisions result in a perceptible or notable change; these successful changes are called successful collisions. The successful collisions must have enough energy, also known as activation energy, at the moment of impact to break the pre-existing bonds and form all new bonds. This results in the products of the reaction. The activation energy is often predicted using the transition state theory. Increasing the concentration of the reactant brings about more collisions and hence more successful collisions. Increasing the temperature increases the average kinetic energy of the molecules in a solution, increasing the number of collisions that have enough energy. Collision theory was proposed independently by Max Trautz in 1916 and William Lewis (physical chemis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Michael Polanyi
Michael Polanyi ( ; ; 11 March 1891 – 22 February 1976) was a Hungarian-British polymath, who made important theoretical contributions to physical chemistry, economics, and philosophy. He argued that positivism is a false account of knowledge, knowing. His wide-ranging research in Outline of physical science, physical science included chemical kinetics, x-ray diffraction, and adsorption of gases. He pioneered the theory of Fiber diffraction, fibre diffraction analysis in 1921, and the dislocation theory of plastic deformation of Ductility, ductile metals and other materials in 1934. He emigrated to Germany, in 1926 becoming a chemistry professor at the Kaiser Wilhelm Institute in Berlin, and then in 1933 to England, becoming first a chemistry professor, and then a social sciences professor at the Victoria University of Manchester, University of Manchester. Two of his pupils won the Nobel Prize, as well as one of his children. In 1944 Polanyi was elected to the Royal Society ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meredith Gwynne Evans
Meredith Gwynne Evans, FRS (2 December 1904 – 25 December 1952) was a British physical chemist who made important contributions to the theory of chemical reaction rates and reaction mechanisms. Together with Henry Eyring and Michael Polanyi, Meredith Gwynne Evans is one of the founders of the transition state theory. Early life and education Meredith Gwynne Evans was born in Atherton, a suburb of Manchester, on 2 December 1904 and the son of Frederick George Evans, an elementary schoolmaster from Pembrokeshire, Wales, and his wife, Margaretta Eleanora Williams. He was the eldest son in a family of three sons and one daughter. Evans attended the elementary school at which his father was Headmaster, won a County Scholarship to Leigh Grammar School, and was educated at the University of Manchester. C. E. H. Bawn, Hugh Taylor, Muriel Tomlinson and Harold Hartley, "Obituary notices: Meredith Gwynne Evans, 1904–1952; James William McBain, 1882–1953; Sydney Glenn Preston Pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
