Overview
This lecture discusses spontaneous endothermic processes and highlights the role of increasing disorder (entropy) in physical and chemical changes.
Examples of Spontaneous Endothermic Processes
- Some endothermic processes are spontaneous, despite requiring energy input.
- Examples include melting of ice (solid water to liquid water), evaporation of water (liquid to gas), and dissolution of sodium chloride in water (solid to aqueous ions).
- All examples involve physical changes (phase changes or dissolving).
Common Features of These Processes
- Each process results in increased disorder (higher entropy) in the system.
- In solids (like ice or salt), particles are arranged in an orderly structure.
- In liquids and aqueous solutions, particles move more freely and are less ordered.
- Gases are even less ordered than liquids; molecules are far apart and move independently.
Order and Disorder in Phase Changes
- Solid phase: molecules are locked in fixed positions (most ordered).
- Liquid phase: molecules move around each other but are still in contact (less ordered).
- Gas phase: molecules are far apart and move freely (least ordered).
- Dissolution: solid salt becomes free-moving ions in solution, increasing disorder.
Nature's Tendency
- Besides favoring lower potential energy, nature also tends toward greater disorder (higher entropy).
Key Terms & Definitions
- Endothermic Reaction — a process that absorbs energy (heat) from its surroundings.
- Spontaneous Process — a process that occurs naturally without continuous external input.
- Entropy — a measure of disorder or randomness in a system.
- Phase Change — transformation from one state of matter to another (e.g., solid to liquid).
Action Items / Next Steps
- Review definitions of entropy and spontaneous processes.
- Consider how entropy changes in additional physical and chemical processes.