IAL Chemistry Kinetics II

Introduction to Chemical Kinetics

• Chemical kinetics measures the speed of reactions and how changing conditions impact it.
• Understanding reaction kinetics can improve various processes.
• Knowing when to hold a reaction at a certain stage is essential to ensure completion before proceeding.
• Certain reagents can enhance specific reaction steps.

Kinetic Rates

• Rate of reaction is defined as the change in concentration of a chemical species over time.
• Measurement techniques for reaction rate include:
  • Volume of gas produced
  • Change in mass
  • Change in concentration
  • Change in color
  • Change in electrical conductivity
  • Change in pH
  • Other measurable physical property changes

Concentration and Rate of Reaction

• The rate of reaction is directly proportional to the concentration of reactants.
• If the concentration of a reactant (e.g., D) doubles, the reaction rate also doubles.
• The relationship can be expressed as:
  • Rate ∝ [D] or Rate = k[D]

Calculating Rate from Graphs

• The gradient of a linear graph directly provides the rate of reaction.
• For nonlinear graphs, calculate the gradient of a tangent drawn at a point.
• Greater triangle sections yield more accurate gradient calculations.

Rate Equation and Orders

• The rate equation connects the rate of reaction to the concentrations of reactants.
• The rate constant (k) is unique to each reaction and varies exclusively with temperature.
• As temperature increases, k increases due to more frequent particle collisions, while concentrations remain constant.

Order of Reaction

• The order of reaction, derived from experimental data, indicates how concentration impacts reaction rate.
• Types of orders include:
  • Zero order: Concentration changes do not affect rate.
  • First order: Rate changes proportionally with concentration change.
  • Second order: Rate changes with the square of the concentration change.
• Overall order is the sum of individual orders, expressed as Overall order = m + n.

Rate Law

• Exponents in the rate law are determined experimentally and are not tied to stoichiometric coefficients.
• Rate equations can include reactants, products, and catalysts, but not intermediates formed during the reaction.

Experimental Determination of Rate Equation

• Initial rate experimental data can be employed to determine the rate equation.
• Rates can be calculated using established rate equations, incorporating the concentration of reactants and the rate constant.

Summary of Concepts

• Rate constant (k) reflects the speed of a reaction; higher values imply faster reactions but remain constant at a given temperature.
• Understanding the various factors affecting reaction rates is essential for practical applications in chemical processes.