Chapter 8: A Journey through States of Water
Explore the fascinating transformation of water between solid, liquid, and gaseous states, evaporation, condensation, cooling effects, and the complete water cycle[cite: 1].
1. Introduction: Ice vs Water
On a bright summer afternoon, Aavi and Thirav enjoy their shikanji (lemonade)[cite: 1]. Looking at the ice in the drink, Thirav wonders if ice and water are completely different substances because ice feels hard to touch while water flows[cite: 1].
"If it does not rain well, even the mighty ocean will be drained." — Thirukkural[cite: 1]
2. Investigating Water's Disappearing Act (Evaporation)
Water puddles in a playground disappear over time[cite: 1]. Water left on washed utensils dries up[cite: 1]. Where does it go?
When water is heated or exposed to air, it converts into a gaseous state called water vapour[cite: 1]. When water is sprinkled on a hot pan, it turns into steam (visible water vapour containing tiny droplets)[cite: 1].
Drying Clothes
Wet clothes dry due to the continuous evaporation of water[cite: 1].
Mopped Floors
Moisture on freshly cleaned floors evaporates quickly into air[cite: 1].
Sweat Cooling
Perspiration on our skin evaporates, cooling our body down[cite: 1, 1].
3. Condensation: The Mystery Droplets
When ice cubes are added to a glass tumbler of cold water, tiny water droplets appear on its outer surface after a few minutes[cite: 1]. Where do these droplets come from?
The water does not seep through the glass wall[cite: 1]! Instead, water vapour present in surrounding air comes into contact with the cold outer surface of the glass tumbler, loses heat, and turns back into liquid water droplets[cite: 1].
4. What are the Different States of Water?
Water exists in three physical states in daily life[cite: 1]:
| Property[cite: 1] | Solid State (Ice)[cite: 1] | Liquid State (Water)[cite: 1] | Gaseous State (Water Vapour)[cite: 1] |
|---|---|---|---|
| Shape[cite: 1] | Fixed shape (retains shape regardless of container)[cite: 1] | No fixed shape (takes container's shape)[cite: 1] | No fixed shape (occupies available space)[cite: 1] |
| Ability to Flow[cite: 1] | Does not flow[cite: 1] | Flows easily[cite: 1] | Diffuses / spreads rapidly[cite: 1] |
| Ability to Spread[cite: 1] | Does not spread[cite: 1] | Spreads while keeping volume constant[cite: 1] | Spreads out in entire available space[cite: 1] |
5. Interconversion of States of Water
Substances change state upon heating or cooling[cite: 1].
6. Factors Affecting Rate of Evaporation
- Exposed Surface Area: Larger surface area speeds up evaporation (water in a plate evaporates faster than in a bottle cap)[cite: 1].
- Temperature / Sunlight: Higher heat increases the rate of evaporation (clothes dry faster on sunny days than in shade)[cite: 1].
- Wind Speed: Increased air movement carries water vapour away faster, accelerating evaporation[cite: 1].
- Humidity: High air moisture content (e.g., rainy days) slows down evaporation[cite: 1].
7. The Cooling Effect of Evaporation
When water evaporates, it absorbs heat energy, producing a cooling effect[cite: 1].
Earthen Pot (Matka/Surahi)
Water seeps through tiny pores in clay pots and evaporates, making stored water cold[cite: 1].
Hand Sanitiser
Sanitiser evaporates rapidly off your hands, producing an immediate cool sensation[cite: 1].
Pot-in-Pot Cooler
An electricity-free refrigerator using wet sand between two earthen pots to preserve food[cite: 1].
8. Cloud Formation & The Water Cycle
Water vapour is lighter than air and rises high into the atmosphere[cite: 1]. As it goes higher, it cools down[cite: 1]. Water vapour condenses around microscopic dust particles to form clouds[cite: 1]. When tiny droplets combine and become heavy, they fall as rain, hail, or snow[cite: 1, 1].
Textbook Exercises Solved
Answer: (iv) The conversion of water vapour into its liquid state[cite: 1].
Answer: (i) (b) water colours & (c) acrylic colours[cite: 1]
(ii) (b) ink pen[cite: 1]
Answer: Natural grass undergoes transpiration (evaporation of water from leaves), which produces a cooling effect in surrounding air[cite: 1]. Plastic grass does not evaporate water[cite: 1].
Answer: Sprinkle water or wipe it with a wet cloth[cite: 1]. The water evaporates rapidly by absorbing heat from the seat, cooling it down quickly[cite: 1].
Interactive MCQ Quiz
Q1. The process of conversion of liquid water into water vapour is called:[cite: 1]
Q2. Water droplets on the outside of an ice-cold glass are caused by:[cite: 1]
Chapter Summary
- Water exists in solid (ice), liquid (water), and gas (water vapour) states[cite: 1].
- Evaporation turns liquid into vapour and requires/absorbs heat[cite: 1].
- Condensation turns vapour into liquid when cooled[cite: 1].
- Evaporation causes a cooling effect[cite: 1].
- The water cycle continually circulates water between Earth and sky[cite: 1].