Key Concepts of Reaction Rate Laws to Know for General Chemistry II

Understanding reaction rate laws is key in General Chemistry II. These laws explain how quickly reactants turn into products, influenced by factors like concentration and temperature. By mastering these concepts, you'll grasp the dynamics of chemical reactions and their practical applications.

1. Definition of reaction rate

   • The reaction rate measures how quickly reactants are converted into products in a chemical reaction.
   • It is typically expressed as the change in concentration of a reactant or product per unit time.
   • Reaction rates can vary based on factors such as concentration, temperature, and the presence of catalysts.

2. Rate law equation

   • The rate law expresses the relationship between the rate of a reaction and the concentration of its reactants.
   • It is generally written in the form: Rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the orders of the reaction with respect to each reactant.
   • The rate law must be determined experimentally and is specific to each reaction.

3. Order of reaction

   • The order of a reaction indicates the power to which the concentration of a reactant is raised in the rate law.
   • It can be zero, first, second, or even fractional, depending on the reaction mechanism.
   • The overall order is the sum of the individual orders of all reactants in the rate law.

4. Rate constant

   • The rate constant (k) is a proportionality factor in the rate law that is specific to a given reaction at a specific temperature.
   • It reflects the speed of the reaction; higher values indicate faster reactions.
   • The rate constant can change with temperature and the presence of catalysts.

5. Zero-order reactions

   • In zero-order reactions, the rate is constant and independent of the concentration of reactants.
   • The rate law takes the form: Rate = k, meaning the reaction proceeds at a constant rate until the reactants are depleted.
   • Common in reactions where a catalyst is saturated or when a surface reaction occurs.

6. First-order reactions

   • First-order reactions have a rate that is directly proportional to the concentration of one reactant.
   • The rate law is expressed as: Rate = k[A], where A is the concentration of the reactant.
   • The half-life of a first-order reaction is constant and independent of concentration.

7. Second-order reactions

   • Second-order reactions can depend on the concentration of one reactant squared or on two different reactants.
   • The rate law can be expressed as: Rate = k[A]^2 or Rate = k[A][B].
   • The half-life of a second-order reaction is inversely proportional to the initial concentration.

8. Half-life

   • The half-life (t½) is the time required for the concentration of a reactant to decrease to half its initial value.
   • It varies depending on the order of the reaction; it is constant for first-order reactions but changes for zero and second-order reactions.
   • Understanding half-life is crucial for predicting how long a reaction will take to reach a certain concentration.

9. Integrated rate laws

   • Integrated rate laws relate the concentration of reactants to time and are derived from the rate laws.
   • They provide equations that allow for the calculation of concentration at any time during the reaction.
   • Different forms exist for zero, first, and second-order reactions, each with its own equation.

10. Method of initial rates

    • This experimental method involves measuring the initial rate of reaction at varying initial concentrations of reactants.
    • It helps determine the order of the reaction with respect to each reactant.
    • By analyzing how the initial rate changes with concentration, the rate law can be established.

11. Arrhenius equation

    • The Arrhenius equation describes how the rate constant (k) changes with temperature (T) and activation energy (Ea).
    • It is expressed as: k = A * e^(-Ea/RT), where A is the pre-exponential factor, R is the gas constant, and T is the temperature in Kelvin.
    • This equation highlights the temperature dependence of reaction rates.

12. Activation energy

    • Activation energy (Ea) is the minimum energy required for a reaction to occur.
    • It influences the rate of reaction; higher activation energies result in slower reactions.
    • The concept is central to understanding how temperature and catalysts affect reaction rates.

13. Collision theory

    • Collision theory states that for a reaction to occur, reactant particles must collide with sufficient energy and proper orientation.
    • The frequency and energy of collisions determine the reaction rate.
    • Factors such as concentration, temperature, and physical state influence the likelihood of effective collisions.

14. Catalysts and their effects on reaction rates

    • Catalysts are substances that increase the rate of a reaction without being consumed in the process.
    • They work by lowering the activation energy required for the reaction to proceed.
    • Catalysts can be homogeneous (in the same phase as reactants) or heterogeneous (in a different phase).

15. Temperature dependence of reaction rates

    • Reaction rates generally increase with temperature due to increased kinetic energy of molecules, leading to more frequent and energetic collisions.
    • The Arrhenius equation quantitatively describes this relationship.
    • Understanding temperature effects is crucial for controlling reaction conditions in practical applications.