reaction rate

(noun)

How fast or slowly a reaction takes place.

Related Terms

  • gas syringe
  • equilibrium
  • concentration
  • product

Examples of reaction rate in the following topics:

  • The Rate Law

    • The rate law for a chemical reaction relates the reaction rate with the concentrations or partial pressures of the reactants.
    • The rate law for a chemical reaction is an equation that relates the reaction rate with the concentrations or partial pressures of the reactants.
    • Lastly, k is known as the rate constant of the reaction.
    • A smaller rate constant indicates a slower reaction, while a larger rate constant indicates a faster reaction.
    • The rate law equation for this reaction is: $Rate = k[NO]^{1}[O_{3}]^{1}$.
  • 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: $\text{rate}=k[H_2][ICl]$.
    • At equilibrium, the rate of the forward reaction will equal the rate of the reverse reaction.
    • Therefore, the rate law must contain no reaction intermediates.
    • Combine elementary reaction rate constants to obtain equilibrium coefficients and construct overall reaction rate laws for reactions with both slow and fast initial steps
  • Chemical Kinetics and Chemical Equilibrium

    • Obviously, there are factors that affect the rates of chemical reactions.
    • Each reaction also has a reaction rate.
    • Reaction rates are not usually constant over a given reaction time.
    • Instead, the reaction rate can be accurately modeled by a rate equation.
    • You can read more about reaction rates and rate laws in the Kinetics unit.
  • Factors that Affect Reaction Rate

    • Raising the concentrations of reactants makes the reaction happen at a faster rate.
    • By doubling the concentration, the rate of reaction has doubled as well.
    • Increasing the pressure for a reaction involving gases will increase the rate of reaction.
    • Similarly, the rate of reaction will decrease with a decrease in temperature.
    • Explore the role of temperature on reaction rate.
  • Measuring Reaction Rates

    • How the rate of a reaction is measured will depend on what the reaction is and what product forms.
    • The following examples describe various ways to measure the rate of a reaction.
    • The rate of a reaction that produces a gas can also be measured by calculating the mass loss as the gas forms and escapes from the reaction flask.
    • In a reaction in which a precipitate is formed, the amount of precipitate formed in a period of time can be used as a measure of the reaction rate.
    • Produce rate expressions when given chemical reactions and discuss methods for measuring those rates
  • Zero-Order Reactions

    • A zero-order reaction has a constant rate that is independent of the concentration of the reactant(s); the rate law is simply $rate=k$ .
    • Unlike the other orders of reaction, a zero-order reaction has a rate that is independent of the concentration of the reactant(s).
    • The rate law for a zero-order reaction is rate = k, where k is the rate constant.
    • In the case of a zero-order reaction, the rate constant k will have units of concentration/time, such as M/s.
    • This is the integrated rate law for a zero-order reaction.
  • Rate Laws for Elementary Steps

    • The rate-determining step is the slowest step in a reaction mechanism.
    • Because it is the slowest, it determines the rate of the overall reaction.
    • However, we cannot simply add the rate laws of each elementary step in order to get the overall reaction rate.
    • Determining the overall reaction rate from the reaction mechanism will be discussed in the next concept.
    • Write rate laws for elementary reactions, explaining how the order of the reaction relates to the reaction rate
  • 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.
    • If this reaction occurred in a single step, its rate law would be:
    • The fact that the experimentally-determined rate law does not match the rate law derived from the overall reaction equation suggests that the reaction occurs over multiple steps.
    • Describe the relationship between the rate determining step and the rate law for chemical reactions
  • Second-Order Reactions

    • If the reaction were second-order in either reactant, it would lead to the following rate laws:
    • The second scenario, in which the reaction is first-order in both A and B, would yield the following rate law:
    • If we are interested in determining the order of the reaction with respect to A and B, we apply the method of initial rates.
    • Therefore, the overall order for the reaction is second-order $(2+0=2)$, and the rate law will be:
    • A table showing data for three trials measuring the various rates of reaction as the initial concentrations of A and B are changed.
  • First-Order Reactions

    • A first-order reaction depends on the concentration of one reactant, and the rate law is: $r=-\frac{dA}{dt}=k[A]$ .
    • Using the Method of Initial Rates to Determine Reaction Order Experimentally
    • Since there is only one reactant, the rate law for this reaction has the general form:
    • By comparing these rates, it is possible for us to find the order of the decomposition reaction.
    • Design initial rate experiments to determine order of reaction with respect to individual reactants
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