Editing Reaction rate (section)

==Temperature dependence==
{{Main|Arrhenius equation}}
Each reaction rate coefficient {{mvar|k}} has a temperature dependency, which is usually given by the [[Arrhenius equation]]:

<math display=block> k = A \exp\left(- \frac{E_\mathrm{a}}{RT} \right)</math>

where 
*{{mvar|A}}, is the pre-exponential factor or [[frequency factor (chemistry)|frequency factor]],
*{{math|exp}} is the [[exponential function]],
*{{math|''E''<sub>a</sub>}} is the activation energy, 
*{{mvar|R}} is the [[gas constant]].
Since at temperature {{mvar|T}} the molecules have energies given by a [[Boltzmann distribution]], [[Arrhenius equation#Kinetic theory's interpretation of Arrhenius equation|one can expect]] the number of collisions with energy greater than {{math|''E''<sub>a</sub>}} to be proportional to <math>\exp\left( \tfrac{-E_{\rm a}}{RT}\right)</math>.

The values for {{mvar|A}} and {{math|''E''<sub>a</sub>}} are dependent on the reaction. There are also more complex equations possible, which describe the temperature dependence of other rate constants that do not follow this pattern.

Temperature is a measure of the average kinetic energy of the reactants. As temperature increases, the kinetic energy of the reactants increases. That is, the particles move faster. With the reactants moving faster this allows more collisions to take place at a greater speed, so the chance of reactants forming into products increases, which in turn results in the rate of reaction increasing. A rise of ten degrees Celsius results in approximately twice the reaction rate.

[[Image:Rxn coordinate diagram 5.PNG|thumb|Reaction coordinate diagram for the bimolecular nucleophilic substitution ([[SN2 reaction|S<sub>N</sub>2]]) reaction between bromomethane and the hydroxide anion|350px]]
The minimum kinetic energy required for a reaction to occur is called the activation energy and is denoted by {{math|''E''<sub>a</sub>}} or {{math|Δ''G''<sup>‡</sup>}}. The transition state or activated complex shown on the diagram is the energy barrier that must be overcome when changing reactants into products. The molecules with an energy greater than this barrier have enough energy to react.

For a successful collision to take place, the collision geometry must be right, meaning the reactant molecules must face the right way so the activated complex can be formed.

A chemical reaction takes place only when the reacting particles collide. However, not all collisions are effective in causing the reaction. Products are formed only when the colliding particles possess a certain minimum energy called threshold energy. As a [[rule of thumb]], reaction rates for many reactions double for every ten degrees Celsius increase in temperature.<ref name="Connors">{{cite book|first=Kenneth |last=Connors|title= Chemical Kinetics:The Study of Reaction Rates in Solution|date= 1990|publisher= VCH Publishers |page=14 |isbn=978-0-471-72020-1}}</ref> For a given reaction, the ratio of its rate constant at a higher temperature to its rate constant at a lower temperature is known as its [[temperature coefficient]], ({{mvar|Q}}).  [[Q10 (temperature coefficient)|''Q''<sub>10</sub>]] is commonly used as the ratio of rate constants that are ten degrees Celsius apart.