rate-determining step

(noun)

The slowest step in a chemical reaction that determines the rate of the overall reaction.

Related Terms

  • consecutive
  • catalysis
  • consumption
  • combustion

(noun)

The slowest individual transformation in a reaction mechanism.

Related Terms

  • consecutive
  • catalysis
  • consumption
  • combustion

Examples of rate-determining step in the following topics:

  • Rate-Determining Steps

    • The rate of a multi-step reaction is determined by the slowest elementary step, which is known as the rate-determining step.
    • In kinetics, the rate of a reaction with several steps is determined by the slowest step, which is known as the rate-determining, or rate-limiting, step.
    • Since the first step is the slowest, and the entire reaction must wait for it, it is the rate-determining step.
    • If the second or a later step is rate-determining, determining the rate law is slightly more complicated.
    • Describe the relationship between the rate determining step and the rate law for chemical reactions
  • Molecularity

    • If a chemical reaction proceeds by more than one step or stage, its overall velocity or rate is limited by the slowest step, the rate-determining step.
    • Once a group gathers at the door, the speed at which other people leave their seats and move along the aisles has no influence on the overall exit rate.
    • When we describe the mechanism of a chemical reaction, it is important to identify the rate-determining step and to determine its "molecularity".
    • The molecularity of a reaction is defined as the number of molecules or ions that participate in the rate determining step.
    • A mechanism in which two reacting species combine in the transition state of the rate-determining step is called bimolecular.
  • Overall Reaction Rate Laws

    • Rate laws for reactions are affected by the position of the rate-determining step in the overall reaction mechanism.
    • Since the first step is the rate-determining step, the overall reaction rate for this reaction is given by this step: $\text{rate}=k[H_2][ICl]$.
    • Step two is the slow, rate-determining step, so it might seem reasonable to assume that the rate law for this step should be the overall rate law for the reaction.
    • We can now substitute this expression into the rate law for the second, rate-determining step.
    • How to determine the rate law for a mechanism with a fast initial step.
  • Steady-State Approximation

    • The steady state approximation can be used to determine the overall rate law when the rate-determining step is unknown.
    • This slowest step determines the rate of the entire reaction, and as such, it is called the rate-determining step.
    • We will now consider cases in which the rate-determining step is either unknown or when more than one step in the mechanism is slow, which affects the overall reaction rate.
    • Before, we assumed that the first step was fast, and that the second step was slow, thereby making it rate-determining.
    • We will now proceed as if we had no such prior knowledge, and we do not know which, if either, of these steps is rate-determining.
  • Rate Laws for Elementary Steps

    • The rate law of the rate-determining step must agree with the experimentally determined rate law.
    • The rate-determining step is the slowest step in a reaction mechanism.
    • The molecularity of the elementary step, and the reactants involved, will determine what the rate law will be for that particular step in the mechanism.
    • For now, just keep in mind that the rate laws for each elementary step are determined by the molecularity of each step only.
    • The molecularity of an elementary step in a reaction mechanism determines the form of its rate law.
  • The Rate Law

    • For the general reaction$aA + bB \rightarrow C$ with no intermediate steps in its reaction mechanism, meaning that it is an elementary reaction, the rate law is given by:
    • The exponents x and y vary for each reaction, and they must be determined experimentally; they are not related to the stoichiometric coefficients of the chemical equation.
    • To reiterate, the exponents x and y are not derived from the balanced chemical equation, and the rate law of a reaction must be determined experimentally.
    • A certain rate law is given as $Rate=k[H_2][Br_2]^\frac{1}{2}$.
    • Note that the reaction order is unrelated to the stoichiometry of the reactions; it must be determined experimentally.
  • Foreign Exchange Rates

    • They calculate the cross rate to determine the exchange rate for these currencies.
    • It does not matter which exchange rates we calculate the cross rate from.
    • Step 1: Trader converts the U.S. dollars to British pounds at Citibank, yielding 64,935.06 £.
    • Step 2: Trader converts the British pounds into euros at Credit Suisse, yielding 103,896.10 €.
    • Step 3: Finally, the trader converts the euros into U.S. dollars at Deutsche bank.
  • Activation Energy

    • Activation energy is the energy required for a reaction to occur, and determines its rate.
    • The reason lies in the steps that take place during a chemical reaction.
    • For this reason, reactant molecules don't last long in their transition state, but very quickly proceed to the next steps of the chemical reaction.
    • The activation energy of a particular reaction determines the rate at which it will proceed.
    • It is determined experimentally.
  • Confidence Interval for a Population Mean, Standard Deviation Not Known

    • Step By Step Example of a Confidence Interval for a Mean—Standard Deviation Unknown
    • Suppose you do a study of acupuncture to determine how effective it is in relieving pain.
    • You measure sensory rates for 15 random subjects with the results given below:
    • We have a sample of 15 rates.
    • We are 95% confident that the interval from 7.30 to 9.15 contains the true mean score of all the sensory rates. 95% of all confidence intervals constructed in this way contain the true mean sensory rate score.
  • Measuring Vendor Performance

    • Firms can measure vendor quality, service, availability, and overall reliability to determine future engagement with the vendor.
    • Decision makers complete five steps when making a business buying decision:
    • Vendor performance measurement plays a role in Steps 3 and 5.
    • Step 3 requires searching for and evaluating possible products and suppliers.
    • Supplier performance evaluation teams are used to monitor activity and performance data, and to rate vendors.
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