6.2 Rate of Reaction

2026 Syllabus Objectives

Core:

  1. Describe the effect on the rate of reaction of:

    • (a) changing the concentration of solutions
    • (b) changing the pressure of gases
    • (c) changing the surface area of solids
    • (d) changing the temperature
    • (e) adding or removing a catalyst, including enzymes

  2. State that a catalyst increases the rate of a reaction and is unchanged at the end of a reaction

  3. Describe practical methods for investigating the rate of a reaction including change in mass of a reactant or a product and the formation of a gas

  4. Interpret data, including graphs, from rate of reaction experiments

Supplement: 5. Describe collision theory in terms of:

  • (a) number of particles per unit volume
  • (b) frequency of collisions between particles
  • (c) kinetic energy of particles
  • (d) activation energy, EaE_a

  1. Describe and explain the effect on the rate of reaction of:

    • (a) changing the concentration of solutions
    • (b) changing the pressure of gases
    • (c) changing the surface area of solids
    • (d) changing the temperature
    • (e) adding or removing a catalyst, including enzymes using collision theory

  2. State that a catalyst decreases the activation energy, EaE_a, of a reaction

  3. Evaluate practical methods for investigating the rate of a reaction including change in mass of a reactant or a product and the formation of a gas

Understanding Reaction Rate ⚡

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Reaction rate is a measure of how fast a chemical reaction takes place. Chemical reactions occur at vastly different speeds:

  • Slow reactions: Rusting of iron, fermentation of sugars to ethanol, enzymatic browning of fruits
  • Fast reactions: Neutralisation reactions, precipitation reactions, combustion reactions, dust explosions

🔑 Key Point: The rate at which a reaction proceeds can be controlled by adjusting various conditions, making this knowledge crucial for both laboratory and industrial processes.

Industrial Hazards: Dust Explosions 💥

The possibility of a dust explosion is a major industrial hazard where fine dusts are present. Any solid material that can burn in air will do so with violence and speed that increases with high degree of subdivision:

  • Coal dust in the atmosphere of mines
  • Flour mills (flour dust)
  • Sugar factories (sugar dust)
  • Wood mills (sawdust)

An accidental spark from machinery can be disastrous. Dust particles have a large surface area relative to their volume in contact with air, making combustion extremely rapid.

Example: Powdered Lycopodium moss piled in a dish does not burn easily, but if the powder is sprayed across a Bunsen flame, it produces a spectacular explosive reaction.

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