Rate of Reaction

1. Definition

  • The rate of reaction measures how quickly reactants change into products.

  • It is expressed as the change in quantity of a reactant or product over time (e.g., g/s, cm³/s).

  • Can be measured through:

    • Change in mass

    • Volume of gas produced

    • Formation of a precipitate

    • Color change

2. Calculating Reaction Rate

  • Average rate = Δ(quantity of reactant or product) ÷ Δ(time)

  • Instantaneous rate = Gradient of a tangent on a concentration-time graph

3. Factors Affecting Rate of Reaction

Factor

How It Affects Rate

Temperature

Higher temperature → particles move faster → more frequent and energetic collisions → increased rate

Concentration

Higher concentration → more particles per volume → more collisions → faster rate

Surface Area

Smaller particle size → larger surface area → more exposure → faster reaction

Catalyst

Lowers activation energy → makes collisions more effective → speeds up reaction without being used up

Pressure (gas)

Higher pressure → particles are closer together → more collisions → faster reaction (for gases only)

4. Collision Theory

  • Particles must collide with enough energy and in the correct orientation to react.

  • The activation energy (Ea) is the minimum energy needed for a successful reaction.

5. Energy Profile & Catalysts

  • Energy profile diagrams show energy changes during a reaction.

  • Catalysts lower the activation energy "hill", allowing the reaction to proceed faster.6. Applications in Daily Life

  • Cooking: High temperature speeds up cooking.

  • Food spoilage: Slower at low temperatures (e.g., refrigeration).

  • Rusting: Can be slowed down by coatings or removing moisture.

  • Digestion: Enzymes act as natural catalysts.

  • Industrial Use:

    • Haber Process: Iron catalyst

    • Contact Process: Vanadium(V) oxide (V₂O₅) catalyst

✅ Quick Summary

  • Rate = Δ(quantity) ÷ Δ(time)

  • Main factors: Temperature, Concentration, Surface Area, Catalyst, Pressure

  • Collision theory: Effective collisions = reaction

  • Catalyst: Speeds up reaction by lowering activation energy

  • Real-life applications: Found in food, health, industry, and nature