Overview
This lecture explains exothermic and endothermic reactions, demonstrates how to represent them with reaction profiles, and covers the concept of activation energy.
Exothermic Reactions
- Exothermic reactions transfer energy to the surroundings, usually as heat.
- In these reactions, products have less stored chemical energy than reactants.
- Heat is released, so the temperature of the surroundings increases.
- Combustion, neutralization, and most oxidation reactions are exothermic.
- On a reaction profile, products are shown lower than reactants to indicate energy release.
Endothermic Reactions
- Endothermic reactions absorb energy from the surroundings, typically as heat.
- Products have more stored chemical energy than reactants.
- Heat is taken in, so the temperature of the surroundings decreases.
- An example is the decomposition of calcium carbonate with heat.
- On a reaction profile, products are placed higher than reactants to show energy absorption.
Reaction Profiles
- The y-axis represents total energy; the x-axis shows reaction progress.
- Exothermic profiles slope downward from reactants to products.
- Endothermic profiles slope upward from reactants to products.
- Energy difference between reactants and products is labeled as "energy released" (exothermic) or "energy absorbed" (endothermic).
Activation Energy
- Activation energy is the minimum energy required for reactant particles to react.
- It is shown on reaction profiles as the peak between reactants and products.
- Even exothermic reactions need some initial energy input.
- Higher curves on the profile indicate higher activation energies.
Key Terms & Definitions
- Exothermic Reaction — Reaction that releases energy to the surroundings, usually as heat.
- Endothermic Reaction — Reaction that absorbs energy from the surroundings.
- Reaction Profile — Diagram showing energy changes during a chemical reaction.
- Activation Energy — Minimum energy needed for reactants to start a reaction.
Action Items / Next Steps
- Practice drawing reaction profiles for exothermic and endothermic reactions, labeling reactants, products, and activation energy.