Energy Changes

• In chemical reactions, energy is not created or destroyed. It is conserved (saved) and transferred between objects
• What are the two types of chemical reactions?

  • Exothermic
  • Endothermic
• Exothermic reaction

  Reaction where energy is released to the surroundings, usually in the form of heat
• Endothermic reaction

  Reaction where energy is absorbed from the surroundings
• Representing reactions using reaction profiles

  1. Plot total energy of molecules on y-axis

  2. Plot progress of reaction on x-axis

  3. Place reactants on left, products on right

  4. Exothermic: products have less energy than reactants

  5. Endothermic: products have more energy than reactants
• Activation energy

  Minimum energy required for reactant particles to collide and react
• Higher activation energy

  More energy required to start the reaction
• Lower activation energy

  Less energy required to start the reaction
• Examples of exothermic reactions

  • Combustion reactions
  • Neutralization reactions between acids and bases
  • Most oxidation reactions
• Energy can't be created or destroyed, it can only be transferred from one place to another
• The most common way to exchange energy with the surroundings is in the form of heat