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Science

How Fast Do Reactions Go?

Overview

Students investigate how temperature, concentration, and surface area affect the speed of a chemical reaction.

Learning Objective
Students understand the factors that affect reaction rate and can explain them in terms of particle collision theory.

Resources needed

  • Bicarbonate of soda
  • Vinegar
  • Hot and cold water
  • Containers

Lesson stages

0 / 7 done
  1. 1 Set up three reaction tests: normal vinegar + bicarbonate; warm vinegar + bicarbonate; diluted vinegar + bicarbonate.
  2. 2 Observe and compare the rate of fizzing in each.
  3. 3 Introduce collision theory: reactions happen when particles collide with enough energy.
  4. 4 Temperature: hotter particles move faster giving more collisions giving faster reaction.
  5. 5 Concentration: more dissolved particles in the same volume giving more frequent collisions giving faster reaction.
  6. 6 Surface area: crush a tablet and dissolve in water — compare with whole tablet. More surface exposed giving more particles colliding giving faster reaction.
  7. 7 Introduce catalysts: substances that speed up reactions without being used up.

Tap a step to mark it as done.

Variations

  • Time how long it takes for a fizzing tablet to dissolve in hot, warm, and cold water.
  • Investigate the effect of surface area on the rate of sugar dissolving.
  • Discuss enzymes as biological catalysts — temperature and pH affect their activity.
More information

Teach: rate, collision, concentration, surface area, temperature, catalyst, enzyme, particle. The phrase more collisions per second is the mechanistic link between each factor and the increased rate.

Focus on one factor — temperature — and establish the collision theory explanation before testing other factors.

Can students explain how increasing temperature affects reaction rate in terms of particle collisions? Can they predict how changing concentration would affect the same reaction?

Vinegar and bicarbonate of soda are cheap and widely available. Hot and cold water demonstrate temperature effects.

Students sometimes think catalysts are used up in the reaction. A true catalyst is regenerated at the end — it lowers the activation energy without being consumed.

Reaction rate chemistry is essential for chemical engineering, cooking, medicine, and environmental science.