Hinglish

Changing the State of Water

Class 6 Science · Chapter 8: A Journey through States of Water · NCERT Curiosity section 8.4

Learn

Take ice from the freezer and leave it in a bowl. It melts into water: solid → liquid. Pure ice melts at 0 °C. Put water in the freezer and it freezes into ice: liquid → solid.

Heat water in a pan. Bubbles grow, and at 100 °C the water boils, changing quickly into water vapour all through the liquid. Cool the vapour and it condenses back into water.

ice ⇄ water ⇄ water vapour (melting/freezing, evaporation/condensation)

Heating changes solid → liquid → gas. Cooling changes gas → liquid → solid. These are changes of state: the substance is still water all along.

Explore: heat and cool the water.

  1. Cool the water until it freezes into ice.
  2. Now heat it until it turns into steam.
  3. Bring it back to liquid water at room temperature (about 25 °C).

Remember

  • Melting (0 °C), freezing, boiling (100 °C), evaporation and condensation are changes of state.
  • Heating: solid → liquid → gas. Cooling: gas → liquid → solid.

Quick check

Water turning into ice is called …

  1. freezing
  2. melting
  3. evaporation
  4. condensation
Answer

freezing. Liquid → solid is freezing.

Think about it

Is boiling the same as evaporation? How are they different?

One answer

Both turn liquid water into vapour. Evaporation happens slowly at any temperature, only from the surface. Boiling happens fast, at 100 °C, with bubbles forming all through the liquid.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.