Back نظرية التصادم Arabic Teoria de les col·lisions Catalan بیردۆزی بەیەکداکەوتن CKB Teorie aktivních srážek Czech Stoßtheorie German Teoría de las colisiones Spanish Aktiivsete põrgete teooria Estonian Talken teoria Basque نظریه برخورد Persian Törmäysteoria Finnish
Collision theory is a principle of chemistry used to predict the rates of chemical reactions. It states that when suitable particles of the 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[1] and William Lewis in 1918.[2] [3]
When a catalyst is involved in the collision between the reactant molecules, less energy is required for the chemical change to take place, and hence more collisions have sufficient energy for the reaction to occur. The reaction rate therefore increases.
Collision theory is closely related to chemical kinetics.
Collision theory was initially developed for the gas reaction system with no dilution. But most reactions involve solutions, for example, gas reactions in a carrying inert gas, and almost all reactions in solutions. The collision frequency of the solute molecules in these solutions is now controlled by diffusion or Brownian motion of individual molecules. The flux of the diffusive molecules follows Fick's laws of diffusion. For particles in a solution, an example model to calculate the collision frequency and associated coagulation rate is the Smoluchowski coagulation equation proposed by Marian Smoluchowski in a seminal 1916 publication.[4] In this model, Fick's flux at the infinite time limit is used to mimic the particle speed of the collision theory. Jixin Chen proposed a finite-time solution to the diffusion flux in 2022 which significantly changes the estimated collision frequency of two particles in a solution.[5]
- ^ Trautz, Max. Das Gesetz der Reaktionsgeschwindigkeit und der Gleichgewichte in Gasen. Bestätigung der Additivität von Cv − 3/2 R. Neue Bestimmung der Integrationskonstanten und der Moleküldurchmesser, Zeitschrift für anorganische und allgemeine Chemie, Volume 96, Issue 1, Pages 1–28, (1916).
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "collision theory". doi:10.1351/goldbook.C01170
- ^ William Cudmore McCullagh Lewis, XLI.—Studies in catalysis. Part IX. The calculation in absolute measure of velocity constants and equilibrium constants in gaseous systems, J. Chem. Soc., Trans., 1918, 113, 471-492.
- ^ Smoluchowski, Marian (1916). "Drei Vorträge über Diffusion, Brownsche Molekularbewegung und Koagulation von Kolloidteilchen". Phys. Z. (in German). 17: 557–571, 585–599. Bibcode:1916ZPhy...17..557S.
- ^ Chen, Jixin (2022). "Why Should the Reaction Order of a Bimolecular Reaction be 2.33 Instead of 2?". J. Phys. Chem. A. 126: 9719–9725. doi:10.1021/acs.jpca.2c07500. PMC 9805503.