Reactivity Reactivity refers to the rate at which a chemical substance tends to undergo a chemical reaction in time. In pure compounds, reactivity is regulated by the physical properties of the sample. For instance, grinding a sample to a higher specific surface area increases its reactivity. In impure compounds, the reactivity is also effected by the inclusion of contaminants. In crystalline compounds, the crystalline form can also affect reactivity. However in all cases, reactivity is primarily due to the sub-atomic properties of the compound. Causes of Reactivity In general, any time a chemical reaction occurs it is due to the chemical being able to enter a more stable state. Quantum chemistry provides the most in depth and exact understanding of the reason this occurs. Electrons exist in orbitals that are the result of solving the Schrodinger equation for specific situations. These orbitals do not exist, and are simply models, however, they provide an excellent basis from which to work. All things (values of the n and ml quantum numbers) being equal, the order of stability of electrons in a system from least to greatest is unpaired with no other electrons in similar orbitals, unpaired with all degenerate orbitals half filled and the most stable is a filled set of orbitals. In order to achieve one of these orders of stability, an atom will react with another atom, thereby stabilizing both atoms. For example, a lone hydrogen atom has a single electron in its 1s orbital. It becomes significantly more stable (as much as 100 kilocalories per mol, or 414 kilojoules per mol) when reacting to form H2. It is for this same reason that carbon will almost always be shown with four bonds. Its ground state valence configuration is 2ss 2p2, not even half filled. However, the activation energy to go from half filled to fully filled p orbitals is so small, it is nearly negligent and as such carbon will form them almost instantaneously, meanwhile the process releases a significant amount of energy (exothermic). Chemical Kinetics and Reactivity The rate of any given reaction A → products (important point is that the order is first) is governed by the equation: $Rate=k[A]$ where the rate is the number of mols/second consumed in the rate-determining step of the reaction, [A] is the concentration of the substance in mol/liter and k is the reaction constant which is constant for that temperature and pressure, though it is independent of concentration. The greater the reactivity of a compound the higher the value of k and the higher the rate. See also catalysis Reactivity series Michaelis-Menten equation organic chemistry chemical kinetics FAVORITE ARTICLES: History of the World    History of the United States    History of Europe    Ancient History    History    Military History    World War I    Bombing of Dresden    California    US Constitution    Frank Sinatra    Boston    Marbury v. Madison This article is licensed under the GNU Free Documentation License at http://www.gnu.org/copyleft/fdl.html You may copy and modify it as long as the entire work (including additions) remains under this license. You must provide a link to http://www.gnu.org/copyleft/fdl.html To view or edit this article at Wikipedia go to http://www.wikipedia.org/wiki/Reactivity