Collision Theory
Related Examples and Practice Problems
Topic Summary & Highlights
and Help Videos
Core Concept
Collision theory states that for a reaction to occur, reactant particles must collide with sufficient energy and proper orientation.
Practice Tips
Link Theory to Observations: Relate concepts to real-world phenomena (e.g., why food spoils faster in the heat).
Use Simulations: Explore interactive models to visualize particle collisions and energy distributions.
Factors Affecting Reaction Rates
1. Nature of Reactants
Influence: Molecules with fewer bonds or weaker bonds react faster.
Examples: Ionic compounds in aqueous solutions react faster than covalent compounds due to the absence of bond-breaking steps.
2. Concentration of Reactants
Influence: Higher concentration increases the number of collisions per second, raising the likelihood of effective collisions.
Key Relationship: Rate ∝ [Reactant]^n, where n is the reaction order.
3. Temperature
Influence: Higher temperatures increase the kinetic energy of particles, leading to:
More frequent collisions.
Greater proportion of collisions with sufficient energy to overcome EaE_aEa.
Rule of Thumb: A 10°C increase in temperature often doubles the reaction rate.
4. Surface Area
Influence: Larger surface area (e.g., powdered solids) increases the exposure of reactants, enhancing collision frequency.
Example: Finely divided catalysts provide more active sites.
5. Catalysts
Definition: Substances that speed up a reaction by lowering the activation energy without being consumed.
Effect:
Provides an alternative pathway with a lower Ea.
Does not affect the energy of reactants or products.
6. Pressure (for Gaseous Reactions)
Influence: Increasing pressure compresses gas particles, leading to more collisions and a faster reaction rate.
Key Insight: Applies only to reactions involving gaseous reactants.
Key Concepts and Terms
Activation Energy (E_a): The minimum energy required for a reaction to occur.
Transition State: A high-energy, unstable state where bonds are partially broken and formed.
Effective Collisions: Collisions that meet the energy and orientation requirements, leading to product formation.
Reaction Rate: The speed at which reactants are converted into products, often expressed as a change in concentration over time.
