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.