6.1 Collision theory and its limitations

Collision theory explains how chemical reactions occur through particle collisions. It states that reactants must collide with enough energy and proper orientation to react. Factors like temperature, concentration, and catalysts affect collision frequency and reaction rates.

While collision theory provides a useful framework, it has limitations. It doesn't account for reaction intermediates, complex mechanisms, or quantum tunneling. These shortcomings led to the development of more comprehensive models like transition state theory.

Here are the updated notes with more detail and following the provided guidelines:

Collision Theory

Principles of collision theory

Top images from around the web for Principles of collision theory

• 

  12.5 Collision Theory | General College Chemistry II View original

  Is this image relevant?

• 

  Collision Theory | Chemistry View original

  Is this image relevant?

• 

  Factors that Affect the Rate of Reactions – Introductory Chemistry – 1st Canadian Edition View original

  Is this image relevant?

• 

  12.5 Collision Theory | General College Chemistry II View original

  Is this image relevant?

• 

  Collision Theory | Chemistry View original

  Is this image relevant?

1 of 3

Top images from around the web for Principles of collision theory

• 

  12.5 Collision Theory | General College Chemistry II View original

  Is this image relevant?

• 

  Collision Theory | Chemistry View original

  Is this image relevant?

• 

  Factors that Affect the Rate of Reactions – Introductory Chemistry – 1st Canadian Edition View original

  Is this image relevant?

• 

  12.5 Collision Theory | General College Chemistry II View original

  Is this image relevant?

• 

  Collision Theory | Chemistry View original

  Is this image relevant?

1 of 3

• States reactant particles must collide with sufficient energy and proper orientation for a reaction to occur
  • Sufficient energy overcomes the activation energy barrier
  • Proper orientation allows formation of new bonds and breaking of old bonds
• Reaction rate depends on frequency of effective collisions between reactant particles
  • Effective collisions have enough energy and proper orientation to lead to a reaction
• Increasing frequency of effective collisions increases the reaction rate

Factors affecting reaction rates

• Temperature
  • Higher temperature increases average kinetic energy of particles
  • More particles have energy greater than activation energy
  • Leads to more effective collisions and faster reaction rate
• Concentration
  • Higher reactant concentration increases particles per unit volume
  • More particles in a given space lead to more frequent collisions
  • Results in higher reaction rate
• Surface area (for heterogeneous reactions)
  • Larger reactant surface area provides more collision sites
  • Increases frequency of effective collisions and reaction rate
• Presence of a catalyst
  • Catalysts lower activation energy barrier
  • More particles have sufficient energy to overcome lowered barrier
  • Leads to increased frequency of effective collisions and faster reaction rate

Limitations of collision theory

• Assumes all collisions with sufficient energy lead to a reaction
  • In reality, not all high-energy collisions result in a reaction due to factors like orientation and presence of reaction intermediates
• Does not account for role of reaction intermediates and complex reaction mechanisms
  • Many reactions proceed through multiple steps involving formation and consumption of intermediate species
  • Does not provide detailed description of these complex mechanisms
• Does not accurately explain temperature dependence of reaction rates
  • Arrhenius equation, $k = Ae^{-E_a/RT}$, better describes relationship between temperature and rate constant
  • Does not derive exponential relationship between temperature and reaction rate
• Does not consider role of quantum mechanical tunneling in some reactions
  • Quantum tunneling allows particles to pass through activation energy barrier instead of overcoming it
  • This phenomenon not accounted for by classical collision theory
• Limitations led to development of transition state theory, which provides more comprehensive description of reaction rates and mechanisms