Rate Law

Definition

The rate law is an expression that describes the relationship between the rate of a chemical reaction and the concentrations of the reactants. It provides a quantitative measure of how the rate of a reaction changes with changes in the concentrations of the reactants involved.

5 Must Know Facts For Your Next Test

1. The rate law is typically expressed in the form: Rate = k[A]^m[B]^n, where k is the rate constant, [A] and [B] are the concentrations of the reactants, and m and n are the reaction orders.
2. The reaction order with respect to a particular reactant indicates the power to which that reactant's concentration is raised in the rate law expression.
3. The rate constant, k, is a measure of the intrinsic reactivity of the reactants and is affected by factors such as temperature, pressure, and the presence of catalysts.
4. The rate law can be determined experimentally by measuring the reaction rate at different initial concentrations of the reactants.
5. The rate law is an important concept in understanding the kinetics and mechanisms of chemical reactions, as it provides insights into the elementary steps involved in the overall reaction.

Review Questions

• Explain how the rate law is used to describe the relationship between reaction rate and reactant concentrations.
  • The rate law is an expression that quantifies the relationship between the rate of a chemical reaction and the concentrations of the reactants involved. It takes the form of Rate = k[A]^m[B]^n, where k is the rate constant, [A] and [B] are the concentrations of the reactants, and m and n are the reaction orders. The reaction orders indicate the sensitivity of the reaction rate to changes in the concentrations of the respective reactants. By understanding the rate law for a given reaction, one can predict how the reaction rate will change as the reactant concentrations are varied, which is crucial for optimizing reaction conditions and understanding reaction mechanisms.
• Describe how the rate constant, k, in the rate law expression is determined and how it relates to the intrinsic reactivity of the reactants.
  • The rate constant, k, in the rate law expression is a measure of the intrinsic reactivity of the reactants under the given reaction conditions. It can be determined experimentally by measuring the reaction rate at different initial concentrations of the reactants and then fitting the data to the rate law expression. The value of the rate constant is affected by factors such as temperature, pressure, and the presence of catalysts, which influence the frequency and efficiency of collisions between the reactant molecules. A higher rate constant indicates a more reactive system, while a lower rate constant suggests a less reactive system. Understanding the factors that affect the rate constant is crucial for controlling and optimizing the kinetics of chemical reactions.
• Analyze how the rate law and reaction order can provide insights into the mechanism of a chemical reaction.
  • The rate law and the associated reaction orders can offer valuable insights into the mechanism of a chemical reaction. The reaction order with respect to a particular reactant indicates the power to which that reactant's concentration is raised in the rate law expression, which reflects the role of that reactant in the rate-determining step of the reaction mechanism. For example, a first-order dependence on a reactant's concentration suggests that the rate-determining step involves the transformation of a single molecule of that reactant. Similarly, a second-order dependence on a reactant's concentration implies that the rate-determining step involves the collision of two molecules of that reactant. By analyzing the rate law and reaction orders, chemists can gain insights into the elementary steps and the overall mechanism of the reaction, which is crucial for understanding and predicting the behavior of chemical systems.

Related terms

Reaction Rate: The rate of a chemical reaction, which is the change in the concentration of reactants or products over time.

Reaction Order: The exponent to which the concentration of a reactant is raised in the rate law expression, indicating the sensitivity of the reaction rate to changes in that reactant's concentration.

Rate Constant: A proportionality constant in the rate law expression that represents the intrinsic reactivity of the reactants and is specific to the given reaction conditions.