This MCQ module is based on: State Changes — Melting, Freezing and Evaporation
TOPIC 28 OF 46
State Changes — Melting, Freezing and Evaporation
🎓 Class 6
Science
CBSE
Theory
Ch 8 — A Journey through States of Water
⏱ ~14 min
🌐 Language: [gtranslate]
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8.4 Water Changes State — The Six Journeys
In Part 1, we saw that water can exist as ice, liquid water, or water vapour. The exciting news is — water can jump from one state to another! All it takes is a little heating or cooling. The six changes (processes) are given special names.
Melting
Solid → Liquid. On heating, ice turns to water at 0 °C.
Freezing
Liquid → Solid. On cooling, water turns to ice at 0 °C.
Evaporation
Liquid → Gas. Happens at any temperature — a puddle drying up in the sun.
Boiling
Liquid → Gas, but fast! Water boils at 100 °C.
Condensation
Gas → Liquid. Steam turns into water drops on a cold lid; dew on leaves.
Sublimation
Solid → Gas directly (no liquid). Camphor, naphthalene balls, dry ice.
Interconversion means changing from one state to another and back again. When you freeze water and then melt the ice, the water has come back — no water was lost!
Activity 8.2 — How Long Does an Ice Cube Take to Melt? L3 Apply
You need: one ice cube, a plate, a watch/clock, a sunny spot and a shady spot.
- Place one ice cube on a plate in the sun. Note the starting time.
- Place another identical cube on a plate in the shade. Note the time.
- Check every 5 minutes. When does each cube disappear completely?
Predict: Which cube will melt faster — the one in the sun or the one in the shade?
The cube in the sun melts much faster because the sunlight gives it more heat. The cube in the shade is cooler and takes longer. This shows that heat is needed to melt ice (solid → liquid). No heat = no melting.
Activity 8.3 — Watch Water Boil L3 Apply
You need: a pan, some water, a gas stove (with adult's help!), a glass plate.
- Pour some water into the pan and place it on a low flame.
- After a while, look at the surface — can you see tiny bubbles? What rises from the pan?
- Hold a cold glass plate (carefully, with tongs) above the steam for 10 seconds. What appears on the plate?
Predict: Why does the plate become wet?
The water evaporates and boils into water vapour (gas). When this hot vapour touches the cold plate, it loses heat and turns back into tiny water drops — that is condensation. You have just seen two state changes in one activity!
Activity 8.4 — The Sweating Glass L3 Apply
You need: a clean, dry glass, very cold water with ice.
- Wipe the outside of the glass with a cloth to make sure it is dry.
- Pour ice-cold water into it. Wait two minutes.
- Look carefully at the outside of the glass.
Predict: Will water come out through the glass? Or from somewhere else?
Tiny water droplets form on the outside of the glass! The glass did not leak. The water vapour in the warm room air touched the cold surface of the glass, lost heat and condensed into water drops. This is the same process that forms dew on leaves in the early morning.
8.5 State-Change Flowchart — Activity 8.5
We can draw all the state-change names on one neat diagram. It shows how water travels between its three homes — solid, liquid, and gas — when we heat it up or cool it down.
8.6 Factors That Control Evaporation
Evaporation can happen slowly or quickly. Four main things speed it up or slow it down.
- Temperature: higher temperature → more evaporation. Clothes dry faster on a hot day.
- Surface area: if you spread water out (like a shirt hung open), more surface touches air, so it evaporates faster. A bunched-up cloth dries slowly.
- Wind: moving air carries away water vapour quickly. A windy day dries clothes faster.
- Humidity: if the air is already full of water vapour (humid), evaporation slows down. That is why clothes dry slowly during the rainy monsoon.
Evaporation Causes Cooling!
Here is a cool trick of nature: when water evaporates, it takes heat from whatever is around it. So the surroundings get cooler! That is why —
- When we sweat after running, the sweat evaporates and carries away body heat, cooling us down.
- A kulhad (clay cup) or matka (earthen pot) has tiny pores. Water seeps out slowly and evaporates from the outside — cooling the water inside. That is why the water in a matka feels cold on a summer day, even with no fridge!
Interactive: State Change Identifier L2
Read each situation and pick the correct process name.
1. A puddle on the road disappears on a sunny day.
2. Water in a tray becomes ice in the freezer.
3. A camphor tablet slowly vanishes from the puja plate.
4. Tiny drops appear on the inside of a window on a cold morning.
5. Butter on toast becomes soft and runny.
Competency-Based Questions
Thirav's mother put a pot of water on the stove to make tea. After some time, Thirav saw small bubbles and steam rising. He also noticed tiny water drops on the lid. Later, his sister placed a tray of water in the freezer to make ice pops, and left a glass of water on the windowsill where it slowly reduced over two days.
Q1. Define melting and evaporation in your own words. L1
Melting is the process where a solid changes into a liquid on heating (e.g. ice → water at 0 °C). Evaporation is the slow change of a liquid into a gas from its surface, and can happen at any temperature.
Q2. Which of these will increase the speed of evaporation? L2
Answer: D. A bigger surface, more heat, and moving air all help evaporation happen faster.
Q3. The drops on the tea-pot lid — which process made them? L2
Condensation. The hot water vapour rose, touched the cooler lid, lost heat, and turned back into tiny water drops.
Q4. Why does wearing wet clothes make us feel extra cold, even on a warm day? L4
Water in the clothes evaporates, and evaporation takes heat from our skin and body. Losing this heat makes us feel cold. The same principle makes sweating cool us after exercise.
Q5. The glass of water on Thirav's windowsill slowly emptied in two days, even without boiling. Explain. L4
The water slowly evaporated from the open surface of the glass. Evaporation happens at any temperature, so even without heat from a flame, the water escaped into the air as invisible water vapour over two days.
Assertion – Reason
Assertion (A): Water in a matka stays cool even without a refrigerator.
Reason (R): Water seeps through the clay pores and evaporates, taking away heat.
Answer: A. Both statements are correct, and evaporation is indeed the reason the water stays cool.
Assertion (A): Boiling and evaporation are the same thing.
Reason (R): Boiling happens only at 100 °C, while evaporation can happen at any temperature.
Answer: D. A is false — boiling and evaporation are different (evaporation is slower and surface-only). R is a correct fact that actually proves A wrong.
Assertion (A): Naphthalene balls in a cupboard slowly disappear.
Reason (R): Naphthalene undergoes sublimation — solid directly turns to gas.
Answer: A. Both are correct. Sublimation is exactly why the naphthalene balls shrink and vanish over time.
Frequently Asked Questions — State Changes — Melting, Freezing and Evaporation
What does the topic 'State Changes — Melting, Freezing and Evaporation' cover in Class 6 Science?
The topic 'State Changes — Melting, Freezing and Evaporation' is part of NCERT Class 6 Science Chapter 8 — A Journey through States of Water. It covers the key ideas of melting, freezing, evaporation, condensation, boiling, state change, heat, explained through everyday examples, labelled diagrams and hands-on activities from the NCERT Curiosity textbook. Class 6 students learn simple definitions, see why each idea matters in daily life, and try short experiments and observations. The lesson uses easy language, colourful pictures and small questions so that young learners build a strong base for higher classes and for competency-based questions in CBSE school tests.
Why is 'State Changes — Melting, Freezing and Evaporation' important for Class 6 NCERT Science?
'State Changes — Melting, Freezing and Evaporation' is important because it builds the first ideas of science that Class 6 students will use again in Class 7, 8 and beyond. NCERT Chapter 8 — A Journey through States of Water — introduces melting and connects it to things children already see at home, at school and in nature. Learning this topic helps students ask better questions, understand simple news about science, and score well in CBSE tests that use competency-based questions. The chapter also supports NEP 2020 by encouraging curiosity, observation and learning by doing rather than only reading and memorising.
What are the key ideas students should remember from State Changes — Melting, Freezing and Evaporation?
The key ideas in 'State Changes — Melting, Freezing and Evaporation' for Class 6 Science are: melting, freezing, evaporation, condensation, boiling, state change, heat. Students should be able to say each term in their own words, give one or two easy examples from daily life, and draw a small labelled diagram where needed. A good way to revise is to make flashcards, write a short note in the science notebook, and solve the NCERT in-text and exercise questions of Chapter 8. Linking every idea to something seen at home or school — in the kitchen, garden, playground or sky — makes these ideas easy to remember for unit tests and the annual CBSE examination.
How is State Changes — Melting, Freezing and Evaporation taught using activities in NCERT Curiosity Class 6?
NCERT Curiosity Class 6 Science teaches 'State Changes — Melting, Freezing and Evaporation' through an inquiry-based approach using Predict–Observe–Explain activities. Students first make a guess, then try a small experiment with safe, easily available materials, and finally explain what happened and why. This matches the NEP 2020 focus on learning by doing. For Chapter 8 — A Journey through States of Water — the textbook has hands-on tasks, labelled pictures and thinking questions built for Bloom's Taxonomy Levels 1 to 6. Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding instead of only rote learning.
What real-life examples of melting can Class 6 students see at home?
Class 6 students can see melting at home in many simple ways linked to 'State Changes — Melting, Freezing and Evaporation'. Kitchens, school bags, playgrounds, the garden and the night sky are full of examples that match NCERT Chapter 8 — A Journey through States of Water. For example, students can look at food labels, watch changes while cooking, try safe activities with water, magnets or shadows, and observe the Sun, Moon and weather each day. Keeping a small science diary — with the date, what was observed and a quick drawing — turns daily life into a mini science lab. These real-life links make concepts easy to remember and help in answering competency-based questions in CBSE Class 6 Science.
How does 'State Changes — Melting, Freezing and Evaporation' connect to other chapters of Class 6 Science?
'State Changes — Melting, Freezing and Evaporation' connects to many other chapters in NCERT Class 6 Science Curiosity. The ideas of melting come back when students study related topics like diversity in the living world, food, magnets, measurement, materials, temperature, water, separation, habitats, natural resources and the solar system. For example, what students learn here helps them build mental pictures for later chapters and for Class 7 and Class 8 Science. Teachers often ask cross-chapter questions in CBSE exams to check if students can use what they learned in Chapter 8 — A Journey through States of Water — in new situations. This linked approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.
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