Steric factor, P[1] is a term used in collision theory. The Collision theory, proposed by Max Trautz and William Lewis in 1916 and 1918 qualitatively explains how Chemical reactions occur and why Reaction
It is defined as the ratio between the experimental value of the rate constant and the one predicted by collision theory. In Chemical kinetics a reaction rate constant k or \lambda quantifies the speed of a Chemical reaction. It can also be defined as the ratio between the preexponential factor and the collision frequency, and it is most often less than unity. See also Arrhenius equation In Chemical kinetics, the preexponential factor or A factor is the pre-exponential constant in the Arrhenius equation See also Collision theory Collision frequency is defined in Chemical kinetics, in the background of theoretical kinetics, as the average number Physically, the steric factor can be interpreted as the ratio of the cross section for reactive collisions to the total collision cross section.
Usually, the more complex the reactant molecules, the lower the steric factors. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Nevertheless, some reactions exhibit steric factors greater than unity: the harpoon reactions, which involve atoms that exchange electrons, producing ions. Harpoon reactions are a type of Chemical reaction between two substances one of them prone to form a Cation, generally a Metal, and the other one prone The deviation from unity can have different causes: the molecules are not spherical, so different geometries are possible; not all the kinetic energy is delivered into the right spot; the presence of a solvent (when applied to solutions). The kinetic energy of an object is the extra Energy which it possesses due to its motion A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. . .
When collision theory applied to reactions in solution the solvent cage has an effect on the reactant molecules, as several collisions can take place in a single encounter, which leads to predicted preexponential factors being too large. The cage effect in Chemistry describes how properties of a Molecule are affected by its surroundings ρ values greater than unity can be attributed to favorable entropic contributions.
Usually there is no simple way to accurately estimate steric factors without performing trajectory or scattering calculations.
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