Question
Compare the three states of matter — solid, liquid, and gas — in terms of shape, volume, compressibility, and particle arrangement. How do substances change from one state to another?
Solution — Step by Step
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes shape of container | Fills entire container |
| Volume | Fixed | Fixed | Not fixed (expands) |
| Compressibility | Very low | Low | High |
| Particle spacing | Very close, orderly | Close but random | Far apart, random |
| Particle motion | Vibrate in place | Slide past each other | Move freely in all directions |
| Density | High | Medium | Low |
Substances change state when we add or remove heat energy:
Special cases:
- Sublimation — solid directly to gas (dry ice, camphor, naphthalene)
- Deposition — gas directly to solid (frost formation)
At the melting point or boiling point, the temperature remains constant even though heat is being added. This heat is used to break intermolecular bonds, not to raise temperature. This energy is called latent heat (latent heat of fusion or vaporisation).
flowchart LR
A[Solid] -->|Melting - heat added| B[Liquid]
B -->|Boiling - heat added| C[Gas]
C -->|Condensation - heat removed| B
B -->|Freezing - heat removed| A
A -->|Sublimation| C
C -->|Deposition| AWhy This Works
All matter is made of particles in constant motion. The state depends on the balance between kinetic energy (movement) and intermolecular forces (attraction). Solids have strong forces and low KE. Gases have weak forces and high KE. Adding heat increases KE until particles overcome forces and change state.
Common Mistake
Students say “ice at 0°C and water at 0°C have the same energy.” They do NOT. Water at 0°C has more energy than ice at 0°C — the extra energy (latent heat of fusion) was used to break the crystal structure of ice. This is why ice at 0°C cools a drink more effectively than water at 0°C.
Camphor, naphthalene balls, and dry ice (solid CO₂) are common examples of sublimation asked in exams. They go directly from solid to gas without passing through the liquid state at normal pressure.