1.7.1Physical Chemistry
Collision Theory — AQA AS Chemistry Revision Notes & Topical Questions
5 min read 4 parts Lesson 40 of 102
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Conditions for Reaction
Collision needed
- Collision needed Particles must collide before a reaction can occur, so the rate depends on how often reacting particles meet.
Activation energy
- Activation energy Colliding particles must have kinetic energy equal to or greater than the activation energy to break the necessary bonds.
Orientation
- Orientation Particles must also hit each other in a suitable orientation so that the right parts of the molecules come into contact.
Successful collision
- Successful collision A successful collision is one that meets both conditions, and only a small fraction of all collisions are successful.
Elastic bounce
- Elastic bounce If the energy is too low or the orientation wrong, particles simply rebound and no reaction takes place.
Part 2 of 4Rate and Collisions
Rate and Collisions
Rate
- Rate The rate of reaction depends on the frequency of successful collisions in a given volume and time.
Frequency
- Frequency Anything that increases the number of collisions per second, such as higher concentration, can raise the rate.
Energy
- Energy Anything that raises the fraction of particles with energy above Ea, such as higher temperature, also raises the rate.
Catalyst
- Catalyst A catalyst increases the proportion of successful collisions by lowering the activation energy needed.
| Change | Effect on collisions |
|---|---|
| Higher concentration | More collisions per second |
| Higher temperature | More collisions and more with E ≥ Ea |
| Catalyst | More collisions succeed because Ea is lower |
Part 3 of 4Writing an Explanation
1
State the change made to the conditions, such as raising the temperature or concentration.
2
Say how this affects the particles, for example more particles per unit volume or particles with higher kinetic energy.
3
Link this to a greater frequency of collisions or a larger fraction of collisions with energy of at least Ea.
4
Conclude that there are more successful collisions per unit time.
5
State that the rate of reaction therefore increases, using the term "frequency of successful collisions".
Part 4 of 4Exam Checklist & Tips
1.7.1 – Key Points for the Exam
- Collision theory The idea that reactions occur when particles collide with enough energy and correct orientation.
- Activation energy The minimum energy colliding particles need in order to react.
- Orientation The way in which colliding particles are positioned relative to one another.
- Rate of reaction The change in concentration of a reactant or product per unit time.
Common Mistakes
- Saying that more collisions always means a faster rate, without noting that they must be successful.
- Writing that particles must have the activation energy, rather than at least the activation energy.
- Ignoring orientation as a requirement for successful collisions.
- Stating that a higher temperature lowers the activation energy; it does not.
Last updated:
\n