Lecture Notes on Exothermic and Endothermic Reactions

Key Concepts

• Chemical Energy Stores: Different chemicals store varying amounts of energy in their bonds.
• Energy Comparison: Important to compare total energy of reactants vs. products.

Reaction Profiles

• Axes:
  • Y-axis: Total energy of molecules
  • X-axis: Progress of the reaction
• Energy Changes:
  • Products with less energy than reactants indicate energy release to surroundings.
  • If products have more energy than reactants, energy is absorbed from surroundings.

Exothermic Reactions

• Definition: Reactions that transfer energy to the surroundings, usually as heat.
• Examples:
  • Combustion reactions (fuels burned with oxygen)
  • Neutralization reactions (acids and bases)
  • Most oxidation reactions
• Reaction Profile:
  • Products lower than reactants on the energy scale.
  • Energy released as heat.

Endothermic Reactions

• Definition: Reactions that absorb heat energy from the surroundings.
• Example:
  • Decomposition of calcium carbonate into calcium oxide and carbon dioxide.
• Reaction Profile:
  • Products higher than reactants on the energy scale.
  • Energy absorbed during the reaction.

Activation Energy

• Definition: Minimum energy needed for reactant particles to collide and react.
• Role in Reactions:
  • Required even for exothermic reactions to begin.
  • Depicted as the energy difference from reactants' energy level to the highest point on the reaction curve.
• Altering Activation Energy:
  • Higher activation energy results in taller energy curves.
  • Lower activation energy results in shorter energy curves.

Drawing Reaction Profiles

• Labeling:
  • Instead of generic "reactants" and "products," use specific chemical names from the reaction equation.

These notes summarize the key aspects of exothermic and endothermic reactions, including how to draw and interpret reaction profiles and the concept of activation energy.