Question
Compare the three states of matter — solid, liquid, and gas — in terms of shape, volume, compressibility, and particle arrangement. Name all the interconversion processes.
(CBSE Class 6 and Class 9 Science)
Solution — Step by Step
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes shape of container | No fixed shape |
| Volume | Fixed | Fixed | Fills entire container |
| Compressibility | Almost incompressible | Slightly compressible | Highly compressible |
| Particle spacing | Very close, tightly packed | Close but can slide | Far apart, randomly moving |
| Particle energy | Lowest | Medium | Highest |
- Melting (solid to liquid): Ice to water at 0 degree C
- Freezing (liquid to solid): Water to ice at 0 degree C
- Evaporation/Boiling (liquid to gas): Water to steam at 100 degree C
- Condensation (gas to liquid): Steam to water
- Sublimation (solid directly to gas): Camphor, dry ice, naphthalene
- Deposition (gas directly to solid): Frost forming on cold surfaces
Adding heat energy causes: melting, evaporation, sublimation (particles move faster, break free from neighbours)
Removing heat energy causes: freezing, condensation, deposition (particles slow down, get closer together)
State Change Flowchart
flowchart LR
A["SOLID"] -->|"Melting (+ heat)"| B["LIQUID"]
B -->|"Freezing (- heat)"| A
B -->|"Evaporation / Boiling (+ heat)"| C["GAS"]
C -->|"Condensation (- heat)"| B
A -->|"Sublimation (+ heat)"| C
C -->|"Deposition (- heat)"| AWhy This Works
The state of matter depends on the kinetic energy of particles relative to the forces between them. In solids, forces dominate — particles vibrate in fixed positions. In liquids, energy and forces are balanced — particles can slide but stay close. In gases, energy wins — particles fly freely.
Temperature is just a measure of average kinetic energy. So when we heat a substance, we give its particles more energy to overcome intermolecular forces, causing a state change.
Common Mistake
Students often forget sublimation — the direct solid-to-gas transition. Camphor (kapoor) is the classic Indian exam example: it turns directly from solid to gas without becoming liquid. Naphthalene balls in your cupboard also sublime over time. For Class 9, remember that sublimation happens when the vapour pressure of the solid exceeds atmospheric pressure before the melting point is reached.