Thermal Physics — Key Terms Enrichment
Master these foundation terms to decode questions quickly. Hover/tap the highlighted terms for quick meanings, and use the examples to anchor ideas to real situations. :contentReference[oaicite:0]{index=0}
Quick Meanings & One-line Hooks
| Term | Student-friendly meaning | One-line example (IGCSE-style) |
|---|---|---|
| Endothermic | Takes in energy (usually heat) from the surroundings. | Ice melting absorbs energy → beaker feels colder. |
| Exothermic | Gives out energy to the surroundings. | Water freezing releases energy → keeps liquid at 0 °C until solidified. |
| Temperature | Indicator of average kinetic energy of particles (°C or K). | At higher T, gas particles collide more → pressure rises at fixed volume. |
| Intermolecular bonds | Attractive forces between particles; must be overcome to melt/boil. | At boiling point, energy breaks attractions instead of raising T. |
| Kinetic energy | Energy due to particle motion; increases as T increases. | Heating a gas → faster particles → more frequent/forceful wall hits. |
| Infra-red radiation | EM waves (IR) that transfer heat; works even in vacuum. | Sun warms Earth via IR; black, matt surfaces absorb/emit best. |
Endothermic vs Exothermic — at a glance
- Endothermic: energy IN to break intermolecular bonds (melting, boiling, sublimation).
- Exothermic: energy OUT as bonds form/strengthen (freezing, condensation, deposition).
Energy in → (break bonds) → state change to less ordered
Energy out → (form bonds) → state change to more ordered
Temperature, Kinetic Energy & Bonding (Particle View)
- Raising temperature → increases average kinetic energy → particles move faster.
- At a flat part of a heating curve (melting/boiling), energy is used to overcome intermolecular bonds, so temperature stays constant.
- Cooling curves: the reverse — energy released as bonds form (exothermic plateaus).
Infra-red Radiation — Surfaces Matter
- Black/dull → better absorber & emitter of IR.
- White/shiny → poorer absorber & emitter; better reflector.
- No medium needed → IR works through a vacuum (space).
Exam Tips
- Use K (Kelvin) for gas-law calculations; convert by
T(K)=T(°C)+273. - On plateaus, write: “Temperature constant because energy changes bonding, not kinetic energy.”
- Always state the direction of energy flow (into system vs out to surroundings) when saying endo/exo.
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