Rates of Reaction
Year 9 ⚗️ Chemical Reactions Describe effects of temperature, concentration, surface area and catalysts on rate.
⏱️ Measuring Rate
Reaction rate = change in amount of reactant or product per unit time.
Rate Formula
$$\text{Rate} = \frac{\text{change in amount (or concentration)}}{\text{time}}$$Ways to measure rate: volume of gas produced (cm³/s), mass lost (g/s), colour change (colorimeter), disappearance of precipitate (cross method).
🔬 Factors Affecting Rate
| Factor | Effect on rate | Why (collision theory) |
|---|---|---|
| ↑ Temperature | Increases | More frequent collisions + more particles have energy ≥ Ea |
| ↑ Concentration | Increases | More particles per volume → more frequent collisions |
| ↑ Surface area | Increases | More particles exposed → more frequent collisions |
| Catalyst added | Increases | Lower activation energy pathway |
| ↑ Pressure (gases) | Increases | Particles closer → more frequent collisions |
💥 Collision Theory & Activation Energy
Conditions for Successful Collision
$$\text{1. Particles must collide} \quad \text{2. Energy} \geq E_a \quad \text{3. Correct orientation}$$ A catalyst provides an alternative pathway with lower Ea — more particles have enough energy to react.
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Interactive Demonstration — Rates of Reaction
⏱️ Rate Calculator
Rate = change in amount ÷ time. Calculate the mean rate from experimental data.