Effect of Concentration on Rate

This lesson covers how changing the concentration of a reactant in solution affects the rate of reaction, with full explanations using collision theory, graphs, and worked examples as required by the Edexcel GCSE Combined Science specification (1SC0).

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The Key Idea

When the concentration of a reactant in solution is increased, there are more particles of that reactant per unit volume. This means the particles are closer together and collisions between reactant particles happen more frequently.

More frequent collisions means more successful collisions per second, so the rate of reaction increases.

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Collision Theory Explanation

graph LR
    subgraph "Low concentration"
        L1["Few particles<br/>per unit volume"]
        L2["Collisions are<br/>less frequent"]
        L3["Fewer successful<br/>collisions/s"]
        L4["Slower rate"]
        L1 --> L2 --> L3 --> L4
    end
    subgraph "High concentration"
        H1["Many particles<br/>per unit volume"]
        H2["Collisions are<br/>more frequent"]
        H3["More successful<br/>collisions/s"]
        H4["Faster rate"]
        H1 --> H2 --> H3 --> H4
    end

    style L4 fill:#c0392b,color:#fff
    style H4 fill:#27ae60,color:#fff

Step-by-step explanation