activation energy
activation energy Symbol
Ea. The minimum energy required for a chemical reaction to take place. In a reaction, the reactant molecules come together and chemical bonds are stretched, broken, and formed in producing the products. During this process the energy of the system increases to a maximum, then decreases to the energy of the products. The activation energy is the difference between the maximum energy and the energy of the reactants; i.e. it is the energy barrier that has to be overcome for the reaction to proceed. The activation energy determines the way in which the rate of the reaction varies with temperature. It is usual to express activation energies in joules per mole of reactants.
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Estimation of liquidus temperatures for multicomponent silicates from activation energies for viscous flow
Magazine article from: Metallurgical and Materials Transactions; 2/1/2000; ; 700+ words
; ...increase in the viscosity and the activation energy for viscous flow. The latter...The second derivative of the activation energy for viscous flow with...temperature dependency of the activation energy to ionic association behavior...
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Thermodynamic view of activation energies of proton transfer in various gramicidin A Channels
Magazine article from: Biophysical Journal; 1/1/2002; ; 700+ words
; ...cations in the SS channel. The activation energies (E^sub a^) for proton transfer...lipid environment. The Gibbs activation free energies (Delta/G^sup...RR channel. In general, the activation entropy (Delta/G^sup...
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Kinetic Analysis of Isothermal Decomposition Process of Sodium Bicarbonate Using the Weibull Probability Function-Estimation of Density Distribution Functions of the Apparent Activation Energies
Magazine article from: Metallurgical and Materials Transactions; 10/1/2009; ; 700+ words
; ...x2264; 0.80, the apparent activation energy (E^sub a^) value was approximately...functions of the apparent activation energies (ddfE^sub a^'s) are not...temperature range, with decomposition activation energy of 85.7 kJmol^sup -1...
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Recrystallization activation energy in mechanically alloyed oxide-dispersion-strengthened metals measured by differential scanning calorimetry
Magazine article from: Metallurgical and Materials Transactions; 7/1/1999; ; 700+ words
; ...alloys with higher activation energy, the recrystallization...due to the very high activation energy of nucleation. The...resulted activation energies are all smaller than...diffusion activation energy. In a theoretical...
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Use of the Activation Energy Concept to Estimate The Quality Reduction of Packaged Olive Oil
Magazine article from: JAOCS, Journal of the American Oil Chemists' Society; 2/1/2005; ; 700+ words
; ...used to comment on the activation energy required during the...70%, the activation energy of an "equivalent...differences between activation energies estimated using the...and of activation energies calculated from it...KEY WORDS: Activation energy, ...
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A correlation method for determination of crystallization mechanism and activation energy of amorphous alloy
Magazine article from: Metallurgical and Materials Transactions; 1/1/1998; ; 700+ words
; ...crystallization mechanism and activation energy of amorphous alloys by investigating...alloys, and the crystallization activation energy is a significant part...determining the crystallization activation energy by measuring the crystallization...
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Numerical solution for Frank-Kamenetskii and activation energy parameters in reactive-diffusive equation with variable one-exponential factor.(Report)
Magazine article from: Journal of Mathematics and Statistics; 10/1/2007; ; 700+ words
; ...effect of Frank-Kamenetskii, activation energy parameter and pre-exponent...molecules. Also, he described the activation energy Ea as the energy which...effects of Frank-Kamenetskii, activation energy parameters and pre-exponent...
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Excitation pressure regulates the activation energy for recombination events in the photosystem II reaction centres of Chlamydomonas reinhardtii.(Report)
Magazine article from: Biochemistry and Cell Biology; 12/1/2007; ; 700+ words
; ...growth conditions decrease the activation energy required for [S.sub.2...no concomitant change in the activation energy for [S.sub.2...croissance diminuent l'energie d'activation requise pour la recombinaison...
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Methods for Calculating Activation Energy for Portland Cement
Magazine article from: ACI Materials Journal; 1/1/2007; ; 700+ words
; ...requires the selection of an activation energy E^sub a^ to define the temperature...equation uses the concept of activation energy E^sub a^ to define...mortar cubes to determine the activation energy for strength estimating...
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Laboratory and Homework Exercises in the Geochemical Kinetics of Mineral-Water Reaction: Rate Law, Arrhenius Activation Energy, and the Rate-Determining Step in the Dissolution of Halite
Magazine article from: Journal of Geoscience Education; 1/1/2004; ; 700+ words
; ...temperature dependence (Arrhenius activation energy) of the reaction...reactions). The chemical-energy difference between the reactant...cannot spontaneously go "up" energy; water does not spontaneously...assemblages. The activation-energy barrier(s) that determine...laws, Arrhenius ...
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activation energy
Book article from: The Columbia Encyclopedia, Sixth Edition
...collisions result in reaction. The activation energy and rate of a reaction are...ex, E a is the activation energy, R is the universal gas constant...reaction rate to activation energy and temperature is exponential...the reaction. Activation energies are usually ...
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energy of activation
Book article from: A Dictionary of Plant Sciences
energy of activation See ACTIVATION ENERGY .
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Neutron Activation Analysis
Encyclopedia entry from: The Gale Encyclopedia of Science
Neutron Activation Analysis Neutron activation analysis is a technique for determining...particle and a gamma ray. The energy associated with the decay process...bombardment. In practice, nuclear activation analysis is carried out by placing...
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neutron-activation analysis
Book article from: A Dictionary of Earth Sciences
neutron-activation analysis The analysis of a material by bombarding a sample with fast-moving...new radionuclides which decay, producing particles with characteristic energies that can be measured with a scintillation counter .
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Mitochondria and Cellular Energy
Book article from: World of Microbiology and Immunology
Mitochondria and cellular energy Mitochondria are cellular organelles...intra-cellular sites where energy is needed. Shape, amount...of eukaryotic cells in the activation of several multiple signal...intracellular enzymatic system activation, active transport of nutrients...
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