Rate Law Determination
Rate Law Determination - Related Videos
10:49
Determining Rate Laws and the Order of Reaction
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2023
Source: Laboratory of Dr. Neal Abrams — SUNY College of Environmental Science and Forestry All chemical reactions have a specific rate defining the progress of reactants going to products. This rate can be influenced by temperature, concentration, and the physical properties of the reactants. The rate also includes the intermediates and transition states that are formed but are neither the reactant nor the product. The rate law defines the role of each reactant in a reaction and can be used to...
03:03
Concentration and Rate Law
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2020
The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions describing the relationship between the rate of a chemical reaction and the concentration of its reactants. For example, in a generic reaction aA + bB ⟶ products, where a and b are stoichiometric coefficients, the rate law can be written as: [A] and [B] represent the molar concentrations of reactants, and k is the rate constant, which is...
03:08
Rate-Determining Steps
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2020
Relating Reaction Mechanisms In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate. The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...
02:39
The Integrated Rate Law: The Dependence of Concentration on Time
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2020
While the differential rate law relates the rate and concentrations of reactants, a second form of rate law called the integrated rate law relates concentrations of reactants and time. Integrated rate laws can be used to determine the amount of reactant or product present after a period of time or to estimate the time required for a reaction to proceed to a certain extent. For example, an integrated rate law helps determine the length of time a radioactive material must be stored for its...
02:33
Rate Law and Reaction Order
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2025
The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions describing the relationship between the rate of a chemical reaction and the concentration of its reactants. For example, in a generic reaction aA + bB ⟶ products, where a and b are stoichiometric coefficients, the rate law can be written as: rate = k[A]m[B]n [A] and [B] represent the molar concentrations of reactants, and k is the rate...
FAQs
Changing one reactant concentration while holding the others constant makes the corresponding rate response easier to interpret. Researchers compare how much the initial rate changes relative to the concentration change, which reveals that reactant’s reaction order. Repeating this comparison for each reactant provides the exponents used in the rate-law expression.
Reaction orders describe how strongly concentration changes affect the reaction rate, whereas the rate constant, k, represents the proportionality factor in the measured relationship. The exponents m and n show the concentration dependence of A and B. Because temperature affects k, temperature must remain controlled when comparing experimental rates.
A measured rate law provides a quantitative pattern for how reactant concentrations influence rate. Researchers can compare that pattern with the behavior expected from plausible reaction mechanisms, using agreement or disagreement to distinguish among them. This makes rate-law analysis relevant not only to measurement, but also to interpreting how a chemical reaction may proceed.
The procedure begins by measuring initial rates for several reaction conditions. In each comparison, one reactant concentration is systematically changed while temperature and the other relevant concentrations remain controlled. Researchers then compare the rate changes, determine reaction orders, calculate the rate constant, and write the resulting concentration relationship as a rate law.
Once the reaction orders and rate constant are known, the rate law can be used to predict how concentration changes affect reaction rate and to anticipate concentration changes over time. These results connect experimental measurements with practical control of reaction conditions, allowing researchers to assess how changing reactant levels may alter the course of a reaction.
Rate-law results support condition optimization in synthetic, industrial, and environmental chemistry. In synthesis, they help evaluate how concentration choices influence reaction behavior. Industrial applications can use the relationship to guide operating conditions, while environmental studies can apply it to predict concentration changes. Across these settings, the measured rate relationship links laboratory data with reaction control.