Overview
This lecture explains how expansion and contraction occur in solids, liquids, and gases at the particle level when heat is added or removed.
Expansion and Contraction Basics
- Adding heat increases particles' kinetic energy, causing them to move further apart.
- The increased space between particles leads to expansion, which occurs in all states of matter.
- Removing heat decreases kinetic energy, so particles move closer together, resulting in contraction.
- The size of individual particles does not change during expansion or contraction.
- These are physical changes; the substance’s identity and particle size remain unchanged.
Expansion and Contraction in Solids
- Heated solids expand because their particles move further apart, not because the particles themselves get bigger.
- Example: A metal ball fits through a ring at room temperature but not after heating due to expansion.
- Gaps in sidewalks and breaks in railway tracks allow for expansion and contraction and prevent cracking.
Expansion and Contraction in Liquids
- Heating a liquid increases particle movement, causing them to spread out and the liquid to take up more space.
- Example: Liquid in a thermometer rises as it expands with heat.
- Classroom experiment: Heated water rises in a thin tube due to expansion.
Expansion and Contraction in Gases
- Gas particles move faster and spread apart when heated, causing expansion.
- Example: A balloon shrinks in the freezer (as gas contracts) and re-expands at room temperature (as gas expands).
Key Terms & Definitions
- Expansion — Increase in a substance’s volume due to particles moving further apart when heated.
- Contraction — Decrease in volume as particles move closer together when cooled.
- Kinetic Energy — The energy particles have due to their motion.
- Physical Change — A change that affects the form of a substance but not its chemical composition.
Action Items / Next Steps
- Review examples of expansion/contraction in daily life (sidewalks, thermometers, balloons).
- Experiment: Try the balloon and freezer demonstration for gases.