Overview
This lecture explains exothermic and endothermic reactions, how to represent them with reaction profiles, and the concept of activation energy.
Exothermic Reactions
- Exothermic reactions release energy to the surroundings, usually as heat.
- In exothermic reactions, the products have less energy than the reactants.
- Reaction profiles for exothermic reactions show products at a lower energy level than reactants.
- The temperature of the surroundings usually increases during exothermic reactions.
- Common examples include combustion, neutralization (acid + base), and most oxidation reactions.
Endothermic Reactions
- Endothermic reactions absorb energy from the surroundings, typically as heat.
- In endothermic reactions, the products have more energy than the reactants.
- Reaction profiles for endothermic reactions place products higher than reactants on the energy axis.
- The temperature of the surroundings usually decreases during endothermic reactions.
- Example: decomposition of calcium carbonate into calcium oxide and carbon dioxide.
Reaction Profiles
- Reaction profiles are diagrams with total energy on the y-axis and reaction progress on the x-axis.
- Reactants are shown on the left and products on the right.
- The vertical difference between reactants and products shows the energy change (released or absorbed).
- Specific chemicals can be labeled instead of generic "reactants" and "products."
Activation Energy
- Activation energy is the minimum energy required for reactant particles to react.
- It is shown on a reaction profile as the energy from reactants to the peak of the curve.
- Both exothermic and endothermic reactions require activation energy to start.
- Curves with higher peaks indicate higher activation energy; lower peaks show lower activation energy.
Key Terms & Definitions
- Exothermic Reaction — A chemical reaction that releases energy to the surroundings, usually as heat.
- Endothermic Reaction — A reaction that absorbs energy from the surroundings, typically as heat.
- Reaction Profile — A diagram showing changes in energy during a chemical reaction.
- Activation Energy — The minimum energy that reactants need to collide and start a reaction.
Action Items / Next Steps
- Practice drawing reaction profiles for both exothermic and endothermic reactions, labeling activation energy.
- Memorize definitions and examples of exothermic and endothermic reactions.