A JOURNEY THROUGH STATES OF WATER : Class 6 : Science
SUMMARY –
Water exists in three states – solid (ice), liquid (water), and gas (water vapour).
It can change from one state to another when heated or cooled.
Melting – Ice changes into water on heating.
Freezing – Water changes into ice on cooling.
Evaporation – Water changes into vapour at all temperatures.
Boiling – Water changes rapidly into vapour at 100°C.
Condensation – Vapour changes into water on cooling.
Sublimation – Some solids like camphor and naphthalene change directly into vapour.
These changes of state are part of nature’s water cycle. Water from oceans, rivers, and lakes evaporates due to the sun’s heat, forms clouds by condensation, and returns to the earth as rain, snow, or hail (precipitation).
Evaporation is faster when temperature is high, wind is strong, or air is dry. It slows down when the air is humid. Evaporation also causes cooling (like sweating cools our body).
Thus, the journey of water through different states is a continuous process that maintains life on earth.
SHORT & LONG QUESTIONS WITH ANSWERS
Q: What are the three states of water?
A: The three states of water are solid (ice), liquid (water), and gas (water vapour).
Q: At what temperature does water freeze?
A: Water freezes at 0°C.
Q: At what temperature does water boil?
A: Water boils at 100°C.
Q: What is evaporation?
A: Evaporation is the process by which liquid water changes into water vapour at all temperatures below boiling.
Q: What is condensation?
A: Condensation is the process of conversion of water vapour into liquid water.
Q: Give one example of condensation from daily life.
A: Water droplets forming on the outside of a cold glass in summer.
Q: What is sublimation?
A: Sublimation is the process by which a solid directly changes into vapour without becoming liquid.
Q: Name a substance that undergoes sublimation.
A: Camphor, naphthalene, and dry ice.
Q: What is melting?
A: The process of change of solid into liquid on heating is called melting.
Q: What is freezing?
A: The process of change of liquid into solid on cooling is called freezing.
Q: What is boiling?
A: The rapid change of liquid into vapour at a fixed temperature is called boiling.
Q: How is boiling different from evaporation?
A: Boiling takes place at a fixed temperature (100°C for water), while evaporation takes place at all temperatures.
Q: Why do clothes dry faster on a windy day?
A: Wind carries away the water vapour, increasing the rate of evaporation.
Q: Why do wet floors take longer to dry on a humid day?
A: Because the air already contains a lot of water vapour, evaporation slows down.
Q: What is condensation responsible for in nature?
A: Formation of dew, fog, clouds, and rain.
Q: Define the water cycle.
A: The continuous circulation of water in nature through evaporation, condensation, and precipitation is called the water cycle.
Q: What role does the sun play in the water cycle?
A: The sun provides heat energy that causes evaporation of water.
Q: What is precipitation?
A: Precipitation is the fall of water from clouds as rain, snow, or hail.
Q: Give two factors affecting evaporation.
A: Temperature and wind speed.
Q: Why is evaporation called a surface phenomenon?
A: Because evaporation takes place only at the surface of the liquid.
Q: What happens to the level of water in a bowl kept in the sun?
A: The water level decreases due to evaporation.
Q: Give an example of sublimation from daily life.
A: Disappearance of naphthalene balls kept in clothes.
Q: How is fog formed?
A: Fog forms when water vapour condenses into tiny water droplets near the ground.
Q: Why does water appear on bathroom mirrors after a hot shower?
A: Because water vapour condenses on the cooler mirror surface.
Q: What is meant by latent heat?
A: The heat energy absorbed or released during a change of state without change in temperature is called latent heat.
Q: Why does sweating cool our body?
A: Sweat evaporates using heat from our skin, making us feel cool.
Q: Name the process responsible for formation of clouds.
A: Condensation.
Q: How does rain occur?
A: Water vapour condenses into tiny droplets that combine and fall as rain.
Q: Why do water droplets form on the outer surface of a water bottle taken out of the fridge?
A: Because water vapour in air condenses on the cold surface of the bottle.
Q: Explain the role of evaporation in the water cycle.
A: Evaporation converts water from rivers, lakes, and oceans into vapour, which rises into the atmosphere.
LONG QUESTION AND ANSWER
1. Question: Explain the three states of water with examples.
Answer: Water exists in three states. As a solid, it is called ice and is found in glaciers and ice cubes. As a liquid, it is simply water that we drink and use daily. As a gas, it is water vapour, which is present in the air. Water can easily change from one state to another due to heating or cooling.
2. Question: Describe the process of melting and freezing with suitable examples.
Answer: Melting is the change of solid water (ice) into liquid water when heat is supplied. For example, ice cubes melt into water at room temperature. Freezing is the reverse process in which liquid water turns into ice when cooled below 0°C. For example, water kept in a freezer turns into ice.
3. Question: Explain evaporation and the factors affecting it.
Answer: Evaporation is the process in which liquid water changes into vapour at all temperatures, not just at boiling point. It is affected by temperature (higher temperature increases evaporation), wind speed (more wind increases evaporation), surface area (larger surface increases evaporation), and humidity (lower humidity increases evaporation).
4. Question: How does evaporation cause cooling? Give examples.
Answer: Evaporation requires heat, which it takes from the surrounding surface. This causes cooling. For example, when we sweat, the sweat evaporates by taking heat from our skin, which cools the body. Similarly, water kept in an earthen pot stays cool because of evaporation from the surface.
5. Question: Differentiate between boiling and evaporation.
Answer: Boiling occurs at a fixed temperature (100°C) when bubbles of vapour form in the liquid. Evaporation occurs at all temperatures, only at the surface of the liquid, and is generally slower. For example, water boils at 100°C to form vapour, while clothes dry due to evaporation at room temperature.
6. Question: Explain condensation with examples from daily life.
Answer: Condensation is the process by which water vapour changes into liquid water on cooling. For example, dew drops form on grass in the morning. Another example is water droplets forming on the outside of a cold glass of water. Clouds are also formed by condensation of water vapour.
7. Question: What is sublimation? Explain with examples.
Answer: Sublimation is the process by which a solid directly changes into vapour without passing through the liquid state. Examples include camphor, dry ice, and naphthalene balls. Dry ice directly changes into carbon dioxide gas, while naphthalene balls slowly vanish when kept in cupboards.
8. Question: Explain the water cycle in detail.
Answer: The water cycle is a continuous process where water circulates between land, air, and water bodies. Water evaporates from oceans, rivers, and lakes into vapour. Vapour condenses to form clouds. Clouds bring precipitation in the form of rain, snow, or hail. This water returns to rivers, lakes, and oceans. The cycle maintains balance of water on Earth.
9. Question: How does humidity affect evaporation?
Answer: Humidity is the amount of water vapour in the air. If the air is already humid, it cannot hold more vapour, so evaporation slows down. On dry days, evaporation is faster as the air can absorb more vapour. That is why clothes dry faster in summer than in the rainy season.
10. Question: Describe the role of evaporation and condensation in the water cycle.
Answer: Evaporation converts water from oceans, rivers, and lakes into vapour. This vapour rises and cools, turning into tiny water droplets through condensation. These droplets form clouds. When clouds become heavy, precipitation occurs. Thus, evaporation and condensation together drive the water cycle.
11. Question: Why do wet clothes dry faster on a sunny and windy day than on a cloudy day?
Answer: On a sunny and windy day, the temperature is higher, and wind speed is more, which both increase evaporation rate. On a cloudy or humid day, evaporation slows down because the air already contains more moisture. Hence clothes dry slowly.
12. Question: Explain with examples how changes of state of water are useful in daily life.
Answer: Ice is used in cooling drinks (solid state). Liquid water is used for drinking, cooking, and cleaning. Steam is used for cooking (in steamers) and running turbines in power stations. Evaporation helps in cooling, drying clothes, and making salt from seawater. Condensation forms rain which is vital for agriculture.
13. Question: What is the difference between boiling and melting?
Answer: Melting is the change of solid to liquid, like ice to water, while boiling is the change of liquid to vapour at its boiling point. Melting occurs at 0°C for ice, while boiling of water occurs at 100°C. Both are physical changes and reversible.
14. Question: Why do we see water droplets on the outside of a glass filled with cold water?
Answer: The air around the glass contains water vapour. When it touches the cold surface of the glass, the vapour cools and condenses into liquid water droplets. This is an example of condensation.
15. Question: Explain why an earthen pot keeps water cool.
Answer: An earthen pot has tiny pores through which water slowly seeps out and evaporates. During evaporation, water absorbs heat from the pot and surroundings, cooling the water inside. That is why water stored in earthen pots is cooler than normal water.
16. Question: Describe the role of temperature in changing the states of water.
Answer: Temperature controls changes of state. On heating, ice melts into water and water boils into vapour. On cooling, vapour condenses into water and water freezes into ice. Thus, heating and cooling are responsible for changes of states.
17. Question: Explain how snow forms in nature.
Answer: Snow is formed when water vapour in the atmosphere condenses into water droplets, which then freeze at very low temperatures to form tiny ice crystals. These ice crystals combine and fall to the ground as snowflakes.
18. Question: How is rain formed in the water cycle?
Answer: Water evaporates from rivers, lakes, and seas. This vapour rises and cools in the atmosphere, condensing into tiny water droplets. These droplets gather to form clouds. When clouds become heavy, they fall as rain.
19. Question: What is precipitation? Explain its different forms.
Answer: Precipitation is the process in which water from clouds falls to the Earth’s surface. It occurs in different forms such as rain, snow, hail, and sleet, depending on the temperature of the atmosphere.
20. Question: How does the water cycle maintain balance in nature?
Answer: The water cycle ensures that water continuously circulates between land, water bodies, and air. Evaporation removes water from the surface, condensation forms clouds, and precipitation returns water to the Earth. This cycle keeps the total amount of water balanced on Earth.
21. Question: Explain with examples how evaporation is useful in our daily life.
Answer: Evaporation is used in drying clothes, cooling water in earthen pots, making salt from seawater, drying food products, and cooling our body through sweating. It is a natural process with many practical uses.
22. Question: Why do water droplets form on the leaves of plants early in the morning?
Answer: In the early morning, the temperature of air decreases, and water vapour condenses on the cool surface of leaves as dew drops. This is condensation in nature.
23. Question: Explain how water changes its state during the process of boiling rice in a cooker.
Answer: When rice is boiled, water absorbs heat and changes into steam (vapour). This steam helps cook the rice. If the cooker is closed, steam condenses back into water, continuing the cycle of evaporation and condensation inside the vessel.
24. Question: How does sublimation differ from evaporation?
Answer: Sublimation is the direct change of solid into vapour, while evaporation is the change of liquid into vapour. Sublimation involves substances like camphor and naphthalene, while evaporation involves water, alcohol, and other liquids.
25. Question: What is the role of the Sun in the water cycle?
Answer: The Sun provides heat energy that causes evaporation of water from oceans, lakes, rivers, and soil. Without the Sun, evaporation and hence the water cycle would not occur.
26. Question: How are clouds formed?
Answer: Clouds are formed when water vapour rises in the atmosphere, cools, and condenses into tiny water droplets. These droplets float in the air, forming clouds.
27. Question: Describe the process of formation of hail.
Answer: Hail forms when raindrops are carried upwards by strong winds into very cold regions of clouds. They freeze into ice pellets and then fall to the ground as hailstones.
28. Question: Why do we see fog in winter mornings?
Answer: In winter, the air is cold, and water vapour near the ground condenses into tiny droplets suspended in the air, forming fog. It is a natural example of condensation.
29. Question: How does water return to the sea after falling as rain on land?
Answer: Rainwater flows into rivers, lakes, and underground water reservoirs. These rivers ultimately flow back to the sea, thus completing the water cycle.
30. Question: Write the importance of the water cycle for life on Earth.
Answer: The water cycle maintains the availability of fresh water, supports plant growth, recharges groundwater, balances temperature through evaporation, and sustains all living beings. Without the water cycle, life would not survive on Earth.
MCQS
Water exists in how many states?
a) One
b) Two
c) Three
d) Four
Answer: c) Three
Which process changes ice into water?
a) Freezing
b) Condensation
c) Melting
d) Sublimation
Answer: c) Melting
Water vapour changing into water is called
a) Evaporation
b) Condensation
c) Freezing
d) Melting
Answer: b) Condensation
The process by which liquid water turns into vapour below boiling point is
a) Boiling
b) Evaporation
c) Freezing
d) Condensation
Answer: b) Evaporation
At what temperature does water boil at sea level?
a) 0°C
b) 50°C
c) 100°C
d) 212°C
Answer: c) 100°C
The process of water changing directly into vapour without becoming liquid is
a) Sublimation
b) Freezing
c) Melting
d) Condensation
Answer: a) Sublimation
Ice changing directly into water vapour is an example of
a) Freezing
b) Sublimation
c) Boiling
d) Condensation
Answer: b) Sublimation
The reverse of evaporation is
a) Boiling
b) Condensation
c) Melting
d) Freezing
Answer: b) Condensation
The process of water vapour cooling into droplets forms
a) Rain
b) Evaporation
c) Boiling
d) Freezing
Answer: a) Rain
Which of the following is not part of the water cycle?
a) Evaporation
b) Condensation
c) Precipitation
d) Combustion
Answer: d) Combustion
Clouds are formed due to
a) Freezing
b) Condensation of water vapour
c) Melting of ice
d) Boiling of water
Answer: b) Condensation of water vapour
Evaporation is faster when
a) Air is humid
b) Temperature is low
c) Wind speed is high
d) Sunlight is absent
Answer: c) Wind speed is high
Evaporation is slower when
a) Temperature is high
b) Air is humid
c) Wind is blowing
d) Air is dry
Answer: b) Air is humid
Which process causes cooling in our body during sweating?
a) Condensation
b) Evaporation
c) Melting
d) Freezing
Answer: b) Evaporation
Water vapour in the atmosphere comes mainly from
a) Rain
b) Oceans and rivers
c) Soil only
d) Plants only
Answer: b) Oceans and rivers
Which of these is an example of condensation?
a) Fog on a cold morning
b) Drying of clothes
c) Boiling water
d) Melting ice
Answer: a) Fog on a cold morning
Water changing into ice is
a) Melting
b) Freezing
c) Evaporation
d) Sublimation
Answer: b) Freezing
The water cycle is driven mainly by
a) Sun’s heat
b) Moon’s gravity
c) Earth’s rotation
d) Plants
Answer: a) Sun’s heat
Rainwater collecting in rivers and lakes is an example of
a) Condensation
b) Collection
c) Freezing
d) Evaporation
Answer: b) Collection
Water changing into vapour during boiling happens at
a) Room temperature
b) 100°C
c) 0°C
d) 25°C
Answer: b) 100°C
Formation of dew is due to
a) Evaporation
b) Melting
c) Condensation
d) Freezing
Answer: c) Condensation
Sublimation of dry ice changes it into
a) Liquid water
b) Water vapour
c) Fog
d) Steam
Answer: b) Water vapour
Evaporation is used in which daily activity?
a) Drying clothes
b) Making ice
c) Freezing food
d) Boiling rice
Answer: a) Drying clothes
Snow changing into water is called
a) Melting
b) Freezing
c) Condensation
d) Evaporation
Answer: a) Melting
Which of the following increases evaporation?
a) High humidity
b) Low wind
c) High temperature
d) Cold weather
Answer: c) High temperature
Fog is an example of
a) Condensation
b) Evaporation
c) Freezing
d) Melting
Answer: a) Condensation
Clouds bring rain through
a) Melting
b) Precipitation
c) Evaporation
d) Boiling
Answer: b) Precipitation
The process that helps in maintaining water balance on Earth is
a) Water cycle
b) Condensation
c) Boiling
d) Freezing
Answer: a) Water cycle
Steam is a form of
a) Solid water
b) Liquid water
c) Water vapour
d) Ice
Answer: c) Water vapour
Which state of water has no fixed shape and volume?
a) Solid
b) Liquid
c) Gas
d) Ice
Answer: c) Gas
Ice cubes left in the open air melt due to
a) Condensation
b) Sublimation
c) Heating from surroundings
d) Freezing
Answer: c) Heating from surroundings
The water droplets on a cold glass of water in summer is due to
a) Freezing
b) Condensation
c) Boiling
d) Evaporation
Answer: b) Condensation
The sun’s heat changes water from oceans into
a) Ice
b) Snow
c) Vapour
d) Steam
Answer: c) Vapour
Evaporation of water from plants is called
a) Boiling
b) Transpiration
c) Condensation
d) Freezing
Answer: b) Transpiration
Water changing from gas to liquid in the water cycle forms
a) Clouds
b) Wind
c) Ocean currents
d) Snowfall only
Answer: a) Clouds
