The Maxwell Boltzmann Distribution | A-level Chemistry | OCR, AQA, Edexcel

Introduction

This tutorial provides an overview of the Maxwell Boltzmann Distribution, an essential concept in A-level Chemistry. Understanding this distribution helps explain molecular behavior in gases, the effects of temperature and catalysts on reaction rates, and how energy distribution influences chemical reactions.

Step 1: Understanding the Maxwell Boltzmann Curve

• The Maxwell Boltzmann Curve illustrates the distribution of molecular energies in a gas at constant temperature.
• Key features of the curve include:
  • The curve starts at the origin, indicating no molecules have zero energy.
  • The area under the curve represents the total number of molecules in the sample.
  • Only molecules with energy greater than the activation energy (Ea) can participate in reactions.

Practical Tip

Visualize the curve to see how molecular speeds vary, where:

• Fast molecules are on the right side of the curve.
• Slow molecules are on the left side.

Step 2: Analyzing the Effect of Temperature

• Increasing the temperature increases the kinetic energy of molecules:
  • The peak of the curve shifts to the right and becomes lower.
  • The overall area under the curve remains constant, indicating the total number of molecules does not change.

Outcomes of Increased Temperature

• Molecules move faster, resulting in:
  • A greater proportion of molecules exceeding the activation energy.
  • An increase in successful collisions over a given time, leading to a higher reaction rate.

Step 3: Exploring the Impact of Catalysts

• Catalysts facilitate reactions by lowering the activation energy:
  • They provide an alternative reaction pathway that requires less energy.
• The addition of a catalyst does not alter the energy distribution of molecules.

Outcomes of Using Catalysts

• More molecules achieve energy levels above the new, lower activation energy, resulting in:
  • An increase in successful collisions.
  • An enhanced rate of reaction.

Step 4: Key Features of the Boltzmann Distribution

• The Boltzmann Distribution graph has notable characteristics:
  • It never touches the x-axis, indicating that no molecules possess zero energy.
  • There is no upper limit on the energy that molecules can have.
  • The area under the curve equals the total number of molecules, reinforcing the concept of conservation.

Conclusion

The Maxwell Boltzmann Distribution is crucial for understanding molecular energy distribution and its relationship with temperature and catalysts. Remember that:

• A higher temperature shifts the curve rightward, increasing reaction rates.
• Catalysts lower activation energy, making reactions more likely without changing the energy distribution.

Next, consider practicing drawing the Maxwell Boltzmann Curve and predicting how it changes with varying temperatures and the presence of catalysts to reinforce your understanding.