Lecture Notes: Chemical Kinetics

Introduction

• Chemical Kinetics: A branch of physical chemistry.
• Focuses on:
  • Rate of reaction
  • Factors affecting the rate of reaction
  • Mechanism of reaction
• Important for board exams.

Key Concepts

Rate of Reaction (ROR)

• Definition: Measure of how fast a chemical reaction occurs, determined by the change in concentration of reactants or products over time.
• Formula:
  • Change in concentration of reactant/product with respect to time.
  • For reactants: Negative sign as the concentration decreases.
  • For products: Positive sign as the concentration increases.

Types of Reactions

• Very Fast Reactions: e.g., Ionic reactions, occur in microseconds, rate not practically measurable.
• Very Slow Reactions: e.g., Rusting of iron, occur over months/years, rate not useful.
• Moderate Reactions: Rate can be measured, focused on in this chapter.

Factors Affecting ROR

• Temperature: Explored through Arrhenius Equation.
• Concentration
• Pressure
• Order of Reaction: First order, second order, etc.
• Rate Law
• Molecularity: Refers to the number of molecules involved in a reaction.

Rate of Reaction: Calculation

Average Rate

• Calculated over a long period of time.
• Formula:
  • ( \text{Average ROR} = -\frac{1}{n} \frac{\Delta [A]}{\Delta t} = \frac{1}{m} \frac{\Delta [B]}{\Delta t} )
  • 'n' and 'm' are stoichiometric coefficients.

Instantaneous Rate

• Calculated for a very small time interval.
• Formula:
  • ( \text{Instantaneous ROR} = -\frac{1}{n} \frac{d[A]}{dt} = \frac{1}{m} \frac{d[B]}{dt} )

Graphical Interpretation

• Slope (tan θ): Represents the rate of change.
• Reactants: Concentration decreases over time.
• Products: Concentration increases over time.

Practical Application

Example Calculations

• Use stoichiometry and changes in concentration to find the rate of reaction.
• Examples include calculating rates using given concentrations and time intervals.

Units of Rate

• Expressed as ( \text{mol L}^{-1} \text{s}^{-1} ) or ( \text{atm s}^{-1} ) for gaseous reactions.

Conclusion

• Understanding different types of rates and how to calculate them is crucial for analyzing reaction kinetics.
• Focus on moderate reactions for practical applications in industries.