Reaction rate constant


Reaction rate constant

In chemical kinetics a reaction rate constant k or λ quantifies the speed of a chemical reaction.[1]

For a chemical reaction where substance A and B are reacting to produce C, the reaction rate has the form:

Reaction: A + B → C
\frac{d[C]}{dt} = k(T)[A]^{m}[B]^{n}

k(T) is the reaction rate constant that depends on temperature.

[C] is the concentration of substance C in moles per volume of solution assuming the reaction is taking place throughout the volume of the solution (for a reaction taking place at a boundary it would denote something like moles of C per area).

The exponents m and n are called orders and depend on the reaction mechanism. They can be determined experimentally.

A single-step reaction can also be written as

\frac{d[C]}{dt} = Ae^\frac{-E_a}{RT}[A]^m[B]^n

Ea is the activation energy and R is the Gas constant. Since at temperature T the molecules have energies according to a Boltzmann distribution, one can expect the proportion of collisions with energy greater than Ea to vary with e-Ea/RT. A is the pre-exponential factor or frequency factor.

The Arrhenius equation gives the quantitative basis of the relationship between the activation energy and the reaction rate at which a reaction proceeds.

Contents

Units

The units of the rate coefficient depend on the global order of reaction:[2]

  • For order n, the rate coefficient has units of mol1-n·Ln-1·s-1
  • For order zero, the rate coefficient has units of mol·L-1·s-1
  • For order one, the rate coefficient has units of s-1
  • For order two, the rate coefficient has units of L·mol-1·s-1

Plasma and gases

Calculation of rate constants of the processes of generation and relaxation of electronically and vibrationally excited particles are of great importance. It is used for example, in the computer simulation of processes in plasma chemistry or microelectronics. First-principle based models should be used for such calculation. It can be done with the help of computer simulation software.

See also

References



Wikimedia Foundation. 2010.

Look at other dictionaries:

  • reaction rate constant — reakcijos spartos konstanta statusas T sritis Standartizacija ir metrologija apibrėžtis Reakcijos, kurios reaguojančių medžiagų koncentracijos yra lygios vienetui, sparta. atitikmenys: angl. reaction rate constant vok. Reaktionskonstante, f rus.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • chemical reaction rate constant — Смотри константа скорости химической реакции …   Энциклопедический словарь по металлургии

  • Reaction rate — Iron rusting a chemical reaction with a slow reaction rate. Wood …   Wikipedia

  • reaction rate — Speed at which a chemical reaction proceeds, in terms of amount of product formed or amount of reactant consumed per unit of time. The reaction rate depends on the nature of the reacting substances and the type of chemical change, as well as… …   Universalium

  • rate constant — a constant of proportionality, k, relating the rate of a single step of a reaction to the concentrations of the reactants, e.g., for a reaction aA + bB ⇄ yY + zZ, the rate (v) = k[A]a[B]b. The rate constant for the forward reaction is kf;… …   Medical dictionary

  • rate constant — reakcijos greičio konstanta statusas T sritis chemija apibrėžtis Reakcijos, kurios reaguojančiųjų medžiagų koncentracijos lygios vienetui, greitis. atitikmenys: angl. rate constant; reaction constant rus. константа скорости реакции; удельная… …   Chemijos terminų aiškinamasis žodynas

  • Rate equation — The rate law or rate equation for a chemical reaction is an equation that links the reaction rate with concentrations or pressures of reactants and constant parameters (normally rate coefficients and partial reaction orders).[1] To determine the… …   Wikipedia

  • Constant (disambiguation) — A constant is something that does not change, over time or otherwise: a fixed value. In most fields of discourse the term is an antonym of variable , but in mathematical parlance a mathematical variable may sometimes also be called a constant.… …   Wikipedia

  • reaction mechanism — Introduction       in chemical reactions (chemical reaction), the detailed processes by which chemical substances are transformed into other substances. The reactions themselves may involve the interactions of atoms (atom), molecules (molecule),… …   Universalium

  • Réaction en chaîne (nucléaire) — Pour les articles homonymes, voir Réaction en chaîne. Schéma d une réaction en chaîne de fission nucléaire 1. Un atome d uranium 235 absorbe un neutron …   Wikipédia en Français


We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.