Navigation Links
Activation energy


The activation energy in chemistry is the energy needed by a system to initiate a particular process. Activation energy is often used to denote the minimum energy needed for a specific chemical reaction to occur. For a reaction to occur between two colliding molecules they must collide in the correct orientation and possess a certain minimum amount of energy. As the molecules approach their electron clouds repel. This requires energy - activation energy - and comes from the heat of the system, i.e. the translational, vibrational, and rotational energy of each molecule. If there is enough energy available, this repulsion is overcome and the molecules get close enough for attractions between the molecules to cause a rearrangement of bonds. The Arrhenius equation gives the quantitative basis of the relationship between the activation energy and the rate at which a reaction proceeds. The study of reaction rates is termed chemical kinetics.


The transition state in a reaction is the point at which the original bonds have stretched to their limit. Transition states are only in existence for extremely brief (10-15 s) periods of time. The energy required to reach the transition state is equal to the activation for that reaction. Multi-stage reactions involve a number of transition points, here the activation energy is equal to the one requiring the most energy. After this time either the molecules move apart again with original bonds reforming, or the bonds break and new products form. This is possible because both possibilities result in the release of energy (shown on the enthalpy profile diagram, Fig. 1, as both positions lie below the transition state). A substance that modifies the transition state to lower the activation energy is termed a catalyst; a biological catalyst is termed an enzyme.


Fig 1. The enthalpy profile of a reaction between two hydrogen peroxide molecules to form water and oxygen. The Transition State is the point at which the original bonds have been stretched as far as they can without breaking (this is illustrated by the structural diagram below the graph.) The energy required to reach the transition state is equal to the activation energy of the reaction.

At low temperatures for a particular reaction most, but not all, molecules will not have enough energy to react. However there will nearly always be a certain number with enough energy at any temperature, because temperature is a measure of the average energy of the system - individual molecules can have more or less energy than the average. Increasing the temperature increases the proportion of molecules with more energy than the activation energy, and consequently the rate of reaction increases. Typically the activation energy is given as the energy in kilojoules needed for one mole of reactants to react.

See also Energy -- Chemical reaction


'"/>


(Date:2/5/2015)... 26, 2015 NXT-ID, Inc. (NASDAQ: NXTD ... authentication company focused on the growing mobile commerce market, ... http://www.nxt-id.com/ ) as part of its 2015 marketing and ... launched its new consumer website for Wocketwallet.com earlier this ... of NXT-ID said, "Our new corporate website naturally showcases ...
(Date:2/5/2015)... 2015 Research and Markets ( ... "Global Biometrics Market (2014-2020): Market Forecast By ... report to their offering. , ... is anticipated to overtake North ... government spending towards IT security, government biometric based ...
(Date:1/22/2015)... Valid S.A. ("Company") (BM&FBOVESPA: VLID3 ON), is pleased to ... State of Washington,s Department of Licensing, in ... central issuance system for driver,s licenses and identification cards to ... and development will start in January 2015, with enrollment and ...
Breaking Biology News(10 mins):NXT-ID, Inc. Launches New Corporate Website As Part Of Ongoing 2015 Branding Initiatives For Wocket Smart Wallet 2NXT-ID, Inc. Launches New Corporate Website As Part Of Ongoing 2015 Branding Initiatives For Wocket Smart Wallet 3Global Biometrics Market (2014-2020): Market Forecast By Technologies, Applications, End Use, Regions and Countries 2Global Biometrics Market (2014-2020): Market Forecast By Technologies, Applications, End Use, Regions and Countries 3Valid USA Signs Contract For Washington Driver's License Issuance 2
... observed and tracked E. coli bacteria moving in a ... paddle. Their findings, which appear online September 29 in the ... better understanding of how bacteria move from place to place and, ... theorized that the cigar-shaped cell bodies of E. coli ...
... ancestors of living cetaceanswhales, dolphins and porpoisesfirst dipped their toes ... ultimately nestled these swimming mammals into the larger hoofed animal ... diet to a carnivorous diet, or the loss of their ... PLoS One resolves this debate using a massive ...
... discoveries in bioengineering become more crucial to fundamental ... supplies, UC San Diego,s Jacobs School of Engineering,s ... the cutting edge of this field. The ... efforts with a $2 million endowment to fund ...
Cached Biology News:Yale engineers track bacteria's kayak paddle-like motion for first time 2Getting a leg up on whale and dolphin evolution 2Getting a leg up on whale and dolphin evolution 3Siebel Foundation awards top UC San Diego bioengineering graduate students 2Siebel Foundation awards top UC San Diego bioengineering graduate students 3Siebel Foundation awards top UC San Diego bioengineering graduate students 4
Other biology definitionOther Tags