Lecture Notes on Effusion and Diffusion

Overview

• Effusion: The process by which gas particles pass through a tiny opening from one container to another.
• Diffusion: The spread of particles from high concentration to low concentration, occurring over time due to random motion.
• Graham's Law: Describes the rates of effusion for different gases.

Effusion

• Mechanism: Particles escape through a pinhole without airflow like a nozzle.
• Rate of Effusion: Proportional to the Root Mean Square (RMS) speed of molecules.
  • RMS speed is dependent on temperature and molar mass.

Graham's Law of Effusion

• Formula: Rate of effusion ∝ 1/√(molar mass).
• Application: Determine the relative rates of effusion between two gases based on their molar masses.
  • Example: Hydrogen (2.016 g/mol) vs. Nitrogen (28.02 g/mol).
  • Hydrogen effuses 3.728 times faster than Nitrogen.

Diffusion

• Characteristics: Similar to effusion but involves spreading in open space.
• Calculation: More complex, often avoids specific calculations in educational settings.
• Demonstration of Diffusion: Ammonia and hydrochloric acid in bottles.
  • NH3 (lighter) diffuses faster than HCl, forming visible NH4Cl cloud on HCl side.

Kinetic Molecular Theory

• Understanding particle behavior in gases, explaining why lighter molecules effuse/diffuse faster.
• Demonstrates practical gas behaviors like effusion and diffusion.

Practical Demonstrations

• Textbook Example: Ammonium hydroxide and hydrochloric acid reaction forming ammonium chloride.
  • Shows faster diffusion of ammonia due to lower molar mass compared to hydrogen chloride.

Conclusion

• Effusion and diffusion are key concepts in molecular kinetics, essential for understanding gas behavior.
• Graham's Law provides a mathematical basis for predicting gas effusion rates.

• Ensure to review textbook figures and examples for better understanding.
• No diffusion calculation questions will be presented due to complexity.