CC6.1 — Rate of reaction (Edexcel 1SC0)
Collision theory
Particles must collide with sufficient energy (≥ activation energy) and the correct orientation for a reaction to occur. These are called successful collisions.
Rate of reaction = number of successful collisions per second.
Factors affecting rate
| Factor | Effect | Explanation |
|---|---|---|
| Temperature | Increases | More kinetic energy → more frequent, more energetic collisions |
| Concentration | Increases | More particles per unit volume → more frequent collisions |
| Surface area | Increases | More particles exposed → more surface for collisions |
| Catalyst | Increases | Provides alternative pathway with lower activation energy |
| Pressure (gases) | Increases | Particles closer together → more frequent collisions |
Measuring rate
- Volume of gas produced vs time (gas syringe or water displacement).
- Mass lost vs time (if gas escapes on balance).
- Colour change vs time (colorimetry).
- Turbidity (cloudiness) for precipitate reactions.
Rate = change in quantity / time taken.
Required practical
Marble chips + HCl: varies surface area (powder vs lumps) or concentration. Measures volume of CO₂ produced over time. Initial gradient = rate.
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