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← Combined Science notes
Edexcel ·Combined Science·Cambridge IGCSE Combined Science

Rates, Energetics & Organic Chemistry

15 min read

Rate of reaction and collision theory, exothermic and endothermic reactions, and an introduction to organic chemistry.

Rate of reaction

The rate of a reaction is how fast reactants are used up or products formed. Collision theory says reactions happen when particles collide with enough energy. Rate increases with:

    Higher temperature — particles move faster and collide more often with more energy.
    Higher concentration / pressure — more particles in a given volume, so more collisions.
    Smaller particle size (larger surface area) — more area for collisions.
    A catalyst — speeds up the reaction (lowers the activation energy) without being used up.

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