To use all functions of this page, please activate cookies in your browser.
With an accout for my.chemeurope.com you can always see everything at a glance – and you can configure your own website and individual newsletter.
- My watch list
- My saved searches
- My saved topics
- My newsletter
Order of reaction
Additional recommended knowledge
For example, given a chemical reaction A + 2B → C with a rate equation r = k[A]1[B]2, the reaction order with respect to A would be 1 and with respect to B would be 2, the total reaction order would be 2+1=3. It is not necessary that the order of a reaction is a whole number - zero and fractional values of order are possible - but they tend to be integers. Reaction orders can be determined only by experiment. Their knowledge allows conclusions about the reaction mechanism.
The reaction order is not necessarily related to the stoichiometry of the reaction, unless the reaction is elementary. Complex reactions may or may not have reaction orders equal to their stoichiometric coefficients
For example :
Zero-order reactions are often seen for thermal chemical decompositions where the reaction rate is independent of the concentration of the reactant (changing the concentration has no effect on the speed of the reaction):
In broken-order reactions the order is a non-integer typical of reactions with a complex reaction mechanism. For example the chemical decomposition of ethanal into methane and carbon monoxide proceeds with an order of 1.5 with respect to ethanal. The decomposition of phosgene to carbon monoxide and chlorine has order 1 with respect to phosgene itself and order 0.5 with respect to chlorine.
In a mixed-order reaction the order of a reaction changes in the course of a reaction as a result of changing variables such as pH. An example is the oxidation of an alcohol to a ketone by a ruthenate (RuO42-) and a hexacyanoferrate, the latter serving as the sacrificial catalyst converting Ru(IV) back to Ru(VI) : the disappearing-rate of the ferrate is zero-order with respect to the ferrate at the onset of the reaction (when its concentration is high and the ruthenium catalyst is quickly regenerated) but changes to first-order when its concentration decreases.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Order_of_reaction". A list of authors is available in Wikipedia.|