Exothermic and Endothermic Reactions

Energy in Chemical Bonds

• Different chemicals store varying amounts of energy in their bonds.
• Example: Methane + Oxygen → Carbon Dioxide + Water.
  • Each molecule holds different energy amounts.

Total Energy of Reactants vs Products

• Key focus: Compare total energy of reactants with that of products.
• Reaction Profile:
  • Y-axis: Total energy of molecules.
  • X-axis: Progress of the reaction.
  • Reactants on the left, products on the right.
  • Products lower down if they have less energy than reactants.

Exothermic Reactions

• Characteristics:
  • Products have less energy than reactants.
  • Energy released to the surroundings, usually as heat.
  • Temperature increase in sealed reactions.
• Common Types:
  • Combustion reactions (fuels + oxygen).
  • Neutralization reactions (acids + bases).
  • Most oxidation reactions.

Endothermic Reactions

• Characteristics:
  • Products have more energy than reactants.
  • Energy absorbed from surroundings.
• Example:
  • Calcium carbonate breakdown using heat.
• Reaction Profile:
  • Products higher than reactants.
  • Energy absorbed labeled in the profile.

Activation Energy

• Definition: Minimum energy required for reactants to collide and react.
• Higher activation energy means more energy needed to start reaction.
• Drawing Activation Energy on Profiles:
  • Curve shows energy change from reactants to products.
  • Activation energy: Difference from reactants' energy level to peak of curve.
• Exothermic reactions require initial energy input despite releasing energy overall.
• Endothermic profiles also show activation energy difference.

Drawing Reaction Profiles

• Use specific chemical equations when labeling reactants and products on profiles.

Summary

• Understand differences between exothermic and endothermic reactions.
• Know how to draw and interpret reaction profiles.
• Remember importance of activation energy in chemical reactions.