Understanding Exothermic and Endothermic Reactions

Learning Objectives

• Define exothermic and endothermic reactions.
• Draw energy profiles for exothermic and endothermic reactions.
• Describe activation energy for a reaction.

Exothermic Reactions

• Definition: Reactions that transfer energy from the reacting molecules to the surroundings.
  • Result: Increase in the temperature of the surroundings (surroundings get hotter).
• Examples:
  • Combustion (e.g., wood burning)
  • Certain oxidation reactions
  • Neutralisation
• Energy Profile:
  • Products have less energy than reactants.
  • Energy released to surroundings is represented by the difference in energy between reactants and products.
• Uses:
  • Hand warmers
  • Self-heating cans (for food or drink)

Endothermic Reactions

• Definition: Reactions that take in energy from the surroundings.
  • Result: Decrease in the temperature of the surroundings (surroundings get colder).
• Example: Thermal decomposition
• Energy Profile:
  • Products have more energy than reactants.
  • Energy taken in is represented by the difference in energy between reactants and products.

Activation Energy

• Concept: Reactions only occur when particles collide with sufficient energy.
• Definition: The minimum amount of energy that particles must have to react.
• Energy Profile Representation:
  • Activation energy is shown from the reactants to the peak of the energy profile curve.
  • Both exothermic and endothermic reactions have an energy rise to a peak, indicating activation energy.

Additional Resources

• More questions and exercises can be found in the revision workbook available via provided links.