Exothermic and Endothermic Reactions

Key Concepts

• Chemical Energy: Different chemicals store different amounts of energy in their bonds.
• Energy Comparison: It is important to compare the total energy of reactants and products.

Reaction Profiles

• Y-Axis: Represents the total energy of molecules.
• X-Axis: Represents the progress of the reaction.
  • Reactants: Placed on the left.
  • Products: Placed on the right.

Exothermic Reactions

• Energy Release: Products have less energy than reactants, energy given off to surroundings.
• Heat Exchange: Most common form of energy transfer is heat.
• Examples:
  • Combustion reactions (burning fuels in oxygen).
  • Neutralization reactions (acids and bases).
  • Most oxidation reactions.

Endothermic Reactions

• Energy Absorption: Products have more energy than reactants, energy absorbed from surroundings.
• Example:
  • Decomposition of calcium carbonate into calcium oxide and carbon dioxide.

Activation Energy

• Definition: Minimum energy required for reactants to collide and react.
• Reaction Profiles:
  • Shown as increase in energy from reactants level to the highest point on the curve.
  • Required even in exothermic reactions to initiate the process.

Drawing Reaction Profiles

• Exothermic Profile: Products lower than reactants; energy released.
• Endothermic Profile: Products higher than reactants; energy absorbed.
• Adjusting Activation Energy:
  • Higher activation energy: Draw higher curves.
  • Lower activation energy: Draw lower curves.

Final Notes

• Instead of labeling lines as 'reactants' and 'products', label with specific chemicals in reaction.
• Useful for exams to understand and draw reaction profiles effectively.

These notes cover the basics of exothermic and endothermic reactions, how to represent them using reaction profiles, and the concept of activation energy.