Effect of Surface Area on Rate

This lesson covers how changing the surface area of a solid reactant affects the rate of reaction, with collision theory explanations, graphs and examples as required by the Edexcel GCSE Combined Science specification (1SC0).

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The Key Idea

When a solid reactant is broken into smaller pieces, its surface area increases. More of the solid's particles are exposed at the surface and are available to collide with particles in the solution (or gas). This means there are more collisions per second, so the rate of reaction increases.

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Collision Theory Explanation

graph LR
    subgraph "Large piece (low SA)"
        LP1["Only outer particles<br/>exposed"]
        LP2["Fewer collisions<br/>per second"]
        LP3["Slower rate"]
        LP1 --> LP2 --> LP3
    end
    subgraph "Powder (high SA)"
        PP1["Many more particles<br/>exposed at the surface"]
        PP2["Many more collisions<br/>per second"]
        PP3["Faster rate"]
        PP1 --> PP2 --> PP3
    end

    style LP3 fill:#c0392b,color:#fff
    style PP3 fill:#27ae60,color:#fff

Step-by-step reasoning