Chemistry · Some Basic Concepts Of Chemistry · NEET
Yes. NCERT says the three states of matter (solid, liquid, gas) are interconvertible by changing the temperature and pressure. The particles stay the same water is still water. Only their spacing and movement change. Add heat and particles move apart; remove heat and they pack together. So ice, liquid water and steam are the same substance in three different states.
Melting is solid changing to liquid at the melting point (example: ice to water at 0 degree C). Boiling is liquid changing to gas at the boiling point (example: water to steam at 100 degree C). Both need heat, but melting is the first change (solid to liquid) and boiling is the second change (liquid to gas). Melting happens at a lower temperature than boiling for the same substance.
No. Both turn a liquid into a gas, but they are not the same. Boiling happens only at the boiling point and happens throughout the whole liquid (bubbles form). Evaporation happens slowly, at any temperature below the boiling point, and only at the surface of the liquid. Example: wet clothes drying is evaporation, not boiling. For NEET, remember: boiling = fixed temperature + bubbles; evaporation = any temperature + surface only.
For a pure substance, yes the numbers are equal. Ice melts at 0 degree C and water freezes at 0 degree C. The difference is only the direction: melting means solid to liquid (heating), freezing means liquid to solid (cooling). Same temperature, opposite process. So melting and freezing are reverse changes of each other.
Sublimation is when a solid changes directly into a gas without becoming a liquid first. It skips the liquid state. Common examples: dry ice (solid carbon dioxide), camphor, naphthalene balls, and iodine crystals. The reverse (gas directly to solid) is called deposition. Sublimation is asked as an example of interconversion, so keep camphor and dry ice ready.
No. Interconversion of states is a physical change, not a chemical change. When ice melts to water, no new substance forms it is still H2O. The chemical composition stays the same; only the physical state changes. This is why boiling point and melting point are called physical properties in NCERT. NEET may test this: state change = physical change, always.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Temperature and pressure. NCERT states the three states are interconvertible by changing these two conditions. Heating or lowering pressure moves matter toward gas; cooling or raising pressure moves it toward solid.
On heating: solid melts to liquid (melting), then liquid boils to gas (boiling/vaporisation). On cooling it reverses: gas condenses to liquid (condensation), then liquid freezes to solid (freezing).
It is a physical change. No new substance is formed; only the physical state changes. The chemical composition stays the same, for example ice, water and steam are all H2O.
Camphor, naphthalene (mothballs), dry ice (solid CO2), and iodine all sublime they go straight from solid to gas without melting into a liquid first.
