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The rate-determining step (RDS) is a chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 term for the slowest step
Reaction step

A reaction step of a chemical reaction is defined as: "An elementary reaction, constituting one of the stages of a stepwise reaction in which a reaction intermediate is converted into the next reaction intermediate in the sequence of intermediates between reactants and products"....
 in a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
. The rate-determining step is often compared to the neck of a funnel; the rate at which water flows through the funnel is determined by the width of the neck, not by the speed at which water is poured in. Similarly, the rate of reaction depends on the rate of the slowest step.

For example, the reaction + ? + can be thought of as occurring in two elementary steps:

  1. + ? + (slow step)
  2. + ? + (fast step)


As the second step consumes the produced in the slow first step, it is limited by the rate of the first step.






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Encyclopedia


The rate-determining step (RDS) is a chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 term for the slowest step
Reaction step

A reaction step of a chemical reaction is defined as: "An elementary reaction, constituting one of the stages of a stepwise reaction in which a reaction intermediate is converted into the next reaction intermediate in the sequence of intermediates between reactants and products"....
 in a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
. The rate-determining step is often compared to the neck of a funnel; the rate at which water flows through the funnel is determined by the width of the neck, not by the speed at which water is poured in. Similarly, the rate of reaction depends on the rate of the slowest step.

For example, the reaction + ? + can be thought of as occurring in two elementary steps:

  1. + ? + (slow step)
  2. + ? + (fast step)


As the second step consumes the produced in the slow first step, it is limited by the rate of the first step. For this reason, the rate-determining step is reflected in the rate equation
Rate equation

The rate law or rate equation for a chemical reaction is an equation which links the reaction rate with concentrations or pressures of reactants and constant parameters ....
 of a reaction.

Another example of a rate-determining step is the formation of a carbocation
Carbocation

A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer Electron shell#Valence shell instead of the eight valence electrons that ensures maximum stability ....
 from a haloalkane
Haloalkane

The haloalkanes are a group of chemical compounds, consisting of alkanes, such as methane or ethane, with one or more halogens linked, such as chlorine or fluorine, making them a type of organic halide....
 during the SN1 reaction
SN1 reaction

The SN1 reaction is a substitution reaction in organic chemistry. "SN" stands for nucleophilic substitution and the "1" represents the fact that the rate-determining step is molecule....
 of tertiary haloalkanes with sodium hydroxide
Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
.

In the previous examples the rate determining step was one of the sequential chemical reactions leading to a product. The rate determining step can also be the transport of reactants to interact and form the product. This case is referred to as diffusion control
Diffusion control

Diffusion-controlled reactions are reactions that occur so quickly that the reaction rate is the rate of transport of the reactants through the reaction medium ....
 and generally occurs where the formation of product from the activated complex is very rapid and thus the supply of reactants and their interaction is rate determining.

The concept of the rate-determining step is very important to the optimization and understanding of many chemical processes such as catalysis
Catalysis

Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
 and combustion
Combustion

Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering....
.

In a reaction coordinate
Reaction coordinate

In chemistry, a reaction coordinate is an abstract one-dimensional coordinate which represents progress along a reaction pathway. It is usually a geometric parameter that changes during the conversion of one or more molecular entity....
, the transition state
Transition state

The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest energy along this reaction coordinate....
 with the highest energy is the rate-determining step of a random reaction.

See also

  • Product-determining step
    Product-determining step

    The product-determining step is the step of a chemical reaction that determines the ratio of product formed via differing reaction mechanisms that start from the same reactants....