chem kinetics 1

Kinetics Overview

  • Definition: Study of reaction rates and the factors affecting them.

  • Important concepts include rate of reaction, empirical observations, order of reaction, and activation energy.

Rate of Reaction

  • The rate of a chemical reaction is influenced by several factors including concentration and temperature.

  • Common expressions for the rate include:

    • Rate Law: [ \text{Rate} = k[A]^m[B]^n ]

      • ( k ): rate constant

      • ( A, B ): reactants

      • ( m, n ): order of reaction with respect to each reactant.

Types of Reactions

  • Spontaneous Reactions: Reactions that occur without external influence, often with negative Gibbs free energy (DG < 0).

  • Explosive Reactions: Fast rate of reaction, typically negative enthalpy change (DG < 0). Examples include nitroglycerin and dynamite.

Testing Techniques

  • Polarimetric Technique: Used to study the inversion of sucrose in acidic solution.

  • Spectroscopic Techniques (fluorescence): Monitor the reaction progress.

  • Electrochemical Techniques: Measure potentials and study concentration changes.

Order of Reaction

  • Overall reaction order is the sum of individual powers:

    • [ q = m + n + o + p ]

  • Example Rate Expression:

    • [ ext{Rate} = k [F]^{x} [CIO_2]^{y} ]

  • Slope related to order of reaction and concentration.

Temperature Dependence of Rate

  • Reaction rates increase with temperature.

  • Arrhenius Equation: Describes the temperature dependence of the rate constant:

    • [ k = A e^{-E_a/(RT)} ]

      • ( A ): pre-exponential factor, ( E_a ): activation energy, ( R ): gas constant, ( T ): temperature.

Activation Energy

  • Minimum energy required for a reaction to occur.

  • Activated Complex: Temporary state during a reaction before products are formed.

  • High activation energy indicates more stability for reactants.

Rate Limiting Step

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

  • Intermediate species may form and decay with time.

Example: Nitroglycerin

  • Notable properties include being sensitive to shock and rapid decay, leading it to be classified as an explosive:

    • Used medically as a vasodilator to treat heart conditions.

    • Explosives require careful handling due to their instability.

Key Chemical Reactions and Dynamics

  • Example Reaction:

    • [ ext{CH}_3 ext{OH} + ext{CC} \rightarrow ext{Products} ]

  • Relationship between concentration, rate of reaction, and temperature influences various reaction dynamics.