Editing Reaction rate constant (section)

{{Short description|Coefficient of rate of a chemical reaction}}

In [[chemical kinetics]], a '''reaction rate constant''' or '''reaction rate coefficient''' ({{tmath|k}}) is a proportionality constant which quantifies the rate and direction of a [[chemical reaction]] by relating it with the concentration of reactants.<ref>{{cite web|title=Chemical Kinetics Notes|url=http://www.chem.arizona.edu/~salzmanr/480a/480ants/chemkine.html|website=www.chem.arizona.edu|access-date=5 May 2018}}</ref>

For a reaction between reactants A and B to form a product C,
{{block indent|em=1.5|text=''a''&nbsp;A + ''b''&nbsp;B → ''c''&nbsp;C}}
where
:A and B are reactants
:C is a product
:''a'', ''b'', and ''c'' are [[stoichiometric coefficient]]s,

the [[reaction rate]] is often found to have the form:

<math display="block">r = k[\mathrm{A}]^m [\mathrm{B}]^{n}</math>

Here {{tmath|k}} is the reaction rate constant that depends on temperature, and [A] and [B] are the [[molar concentration]]s of substances A and B in [[mole (unit)|moles]] per unit volume of solution, [[Presupposition|assuming]] the reaction is taking place throughout the volume of the solution. (For a reaction taking place at a boundary, one would use moles of A or B per unit area instead.)

The exponents ''m'' and ''n'' are called partial [[orders of reaction]] and are ''not'' generally equal to the stoichiometric coefficients ''a'' and ''b''. Instead they depend on the [[reaction mechanism]] and can be determined experimentally. 

Sum of m and n, that is, (''m'' + ''n'') is called the overall order of reaction.