Thermal Energy, Temperature, and States of Matter

Thermal Energy, Temperature, and Heat

• Thermal Energy: The total energy of all the tiny moving particles within an object.

• Temperature: Measures the average movement energy ($KE$) of these particles.

  • More thermal energy = faster particles = higher temperature.

  • Less thermal energy = slower particles = lower temperature.

• Heat: The flow of thermal energy from a warmer thing to a cooler thing.

• Measurement: Thermometers use liquid expansion/contraction to show temperature.

States of Matter and Phase Changes

• Particle Motion:

  • Solid: Particles vibrate in place (low $KE$).

  • Liquid: Particles slide past each other (medium $KE$).

  • Gas: Particles move fast and freely (high $KE$).

• Changing States:

  • Melting: Solid to liquid (particles gain $KE$ and move).

  • Boiling/Vaporization: Liquid to gas (particles gain $KE$ and escape).

  • Evaporation: Liquid to gas from the surface.

  • Condensation: Gas to liquid (particles lose $KE$ and slow down).

  • Freezing: Liquid to solid (particles lose $KE$ and fix in place).

Energy Conservation and Latent Heat

• Law of Conservation of Energy: Energy is never created or destroyed; it just changes form.

• During a phase change (like melting), temperature ($KE$) stays constant even with added thermal energy.

• That added energy becomes potential energy (stored energy), changing how particles are arranged, not how fast they move.

• Thermal energy includes both particle movement energy ($KE$) and stored positioning energy.

• Different materials need different amounts of energy to change phase due to varying particle bond strengths (e.g., glass needs $1400^{\circ}C$, butter needs $32^{\circ}C$ to melt).

Kinetic Molecular Theory (KMT)

• Explains gas behavior with five main ideas:

1. Gas particles are tiny, far apart, have no fixed volume, but have mass.

2. Gas particles don't attract or repel each other.

3. Gas particles are always moving randomly.

4. Collisions between gas particles are elastic (no $KE$ lost).

5. All gases at the same temperature have the same average $KE$ per particle.

• Particle motion stops only at absolute zero, the coldest possible temperature.