5.2.4Additional lessons
Factors Affecting Rates of Reaction — IB Chemistry SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 69 of 98
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.
Section 1 of 4Concentration and Pressure
Each factor changes either how often particles collide or how many have enough energy.
Concentration
- Concentration A higher concentration of a reactant in solution means more particles per unit volume,
- so collisions are more frequent and the rate rises.
Gas pressure
- Gas pressure Increasing the pressure of a gas squeezes the molecules closer together, so concentration and collision frequency increase.
No change in energy
- No change in energy Neither change alters the fraction of particles with enough energy;
- only the collision frequency is affected.
Limit
- Limit As reactants are used, concentration decreases and the rate slows over time.
Section 2 of 4Surface Area and Temperature
Surface Area and Temperature
Surface area
- Surface area Crushing a solid exposes more particles to the other reactant, which increases collision frequency and the rate.
Examples
- Examples Powdered calcium carbonate reacts faster with acid than marble chips of the same mass.
Temperature
- Temperature Particles move faster and have more kinetic energy, so there are more frequent collisions.
Greater effect
- Greater effect The main effect is that a much larger fraction of particles has energy equal to or greater than the activation energy.
Section 3 of 4Catalysts
1
A catalyst is a substance which speeds up a reaction without being permanently used up.
2
It provides an alternative reaction pathway with a lower activation energy.
3
A greater proportion of collisions then has sufficient energy, so the rate increases.
4
The catalyst is regenerated at the end of the reaction, and it does not change the enthalpy change or the amount of product.
Section 4 of 4Exam Checklist & Tips
5.2.4 – Key Points for the Exam
- Catalyst A substance which increases the rate of a reaction by providing an alternative pathway of lower activation energy, and is not used up.
- Surface area The total area of solid exposed and available for reaction.
- Concentration The amount of substance per unit volume.
- Activation energy The minimum energy needed for a successful collision.
Common Mistakes
- Saying that a catalyst is not involved in the reaction; it takes part but is regenerated.
- Explaining a temperature effect only through more frequent collisions.
- Stating that a catalyst increases the energy of the particles.
- Saying that more surface area increases the activation energy or the yield.
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