States of Matter and Change of State
NCERT Class 9 • Science • Chapter "Matter in Our Surroundings" | NCERT Class 6 • Science • Chapters on materials
States of Matter and Change of State
Matter is anything that has mass and occupies space. It is made of very small particles that have space between them, attract one another and are always in motion. The three common states — solid, liquid and gas — differ only in how strongly those particles are held together.
The Three States
- Solids have a fixed shape and fixed volume; particles are tightly packed with strong force of attraction and vibrate in place.
- Liquids have a fixed volume but take the shape of the container; particles are less tightly held and can slide past one another.
- Gases have neither fixed shape nor fixed volume; particles are far apart with negligible attraction and move very fast.
- Compressibility is highest in gases, very small in liquids and almost nil in solids.
- Diffusion, the mixing of particles on their own, is fastest in gases and slowest in solids.
- Density is generally highest in solids and lowest in gases.
- Plasma and Bose Einstein condensate are additional states studied beyond the common three.
Change of State
- Melting is solid to liquid, and the temperature at which it happens at atmospheric pressure is the melting point.
- Boiling is liquid to gas throughout the liquid at the boiling point; evaporation is a surface phenomenon at any temperature.
- Condensation is gas to liquid and freezing is liquid to solid.
- Sublimation is the direct change from solid to gas, as in camphor, naphthalene, ammonium chloride and dry ice.
- Latent heat is the heat absorbed or released during a change of state without any change of temperature.
- Evaporation causes cooling because the fastest particles leave the surface, taking energy with them.
- Evaporation increases with higher temperature, larger surface area, lower humidity and faster wind.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes container shape | Fills container |
| Volume | Fixed | Fixed | Not fixed |
| Compressibility | Almost nil | Very small | High |
| Rate of diffusion | Very slow | Moderate | Very fast |
Latent heat — the heat absorbed or given out during a change of state without any change in temperature.
Hindi me samjhein
वाष्पीकरण सतह से किसी भी तापमान पर होता है, जबकि उबलना क्वथनांक पर पूरे द्रव में होता है। इसीलिए गर्मी में पानी बिना उबले भी सूख जाता है।
Exam me kaise aata hai
- Direct change from solid to gas is called — sublimation
- Heat absorbed during change of state without temperature change is — latent heat
- Which state has the highest compressibility — gas
- Evaporation is a phenomenon of the — surface
UPSC/State PSC ke liye
- The temperature stays constant during melting and boiling because the supplied heat goes into overcoming the force of attraction, not into raising particle speed.
- A pressure cooker works because raising pressure raises the boiling point, so water stays liquid at a higher temperature and cooks food faster.
Yahan confuse hote hain
✗ Evaporation and boiling are the same | Evaporation is a surface effect at any temperature; boiling happens at the boiling point throughout | ✓
✗ Temperature rises during melting | Temperature stays constant; the heat is latent heat | ✓
✗ Gases have fixed volume | Gases have neither fixed shape nor fixed volume | ✓
Ek nazar me
- Matter is made of moving particles with space and attraction between them.
- Solid, liquid and gas differ in packing, shape, volume and compressibility.
- Sublimation goes directly from solid to gas.
- Latent heat is absorbed during change of state without temperature change.