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
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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 = A e − E a / R T k = Ae^{-E_a/RT} k = A e − 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