Matter in Our Surroundings
Question Paper (Total Marks: 80) | Time: 2.5 Hours
Section A: Multiple Choice Questions (1 Mark Each) [Total: 10 Marks]
1 Mark
Q1. Which of the following is NOT matter?
a) Air
b) Water
c) Love
d) Iron
Answer: c) Love
Explanation:
Matter is defined as anything that has mass and occupies space. Love is an emotion and doesn't have mass or occupy space, so it's not matter. Air, water, and iron all have mass and occupy space.
1 Mark
Q2. The SI unit of volume is:
a) Litre
b) Cubic metre
c) Millilitre
d) Centimetre
Answer: b) Cubic metre (m³)
Explanation:
The SI unit of volume is cubic metre (m³). While litre (1L = 1 dm³) is commonly used, the SI unit is m³.
1 Mark
Q3. Which state of matter has the strongest intermolecular forces?
a) Gas
b) Liquid
c) Solid
d) Plasma
Answer: c) Solid
Explanation:
In solids, the forces of attraction between particles are maximum, which keeps them fixed in definite positions. Liquids have intermediate forces, and gases have minimum forces.
1 Mark
Q4. The process of change from liquid to gas is called:
a) Condensation
b) Vaporization
c) Sublimation
d) Freezing
Answer: b) Vaporization
Explanation:
Vaporization is the process of change from liquid state to gaseous state. It can occur at the boiling point (boiling) or below (evaporation).
1 Mark
Q5. The melting point of ice is:
a) 273 K
b) 373 K
c) 100°C
d) 373°C
Answer: a) 273 K (or 0°C)
Explanation:
The melting point of ice is 273.15 K (approximately 273 K), which is 0°C. At this temperature at atmospheric pressure, ice converts to water.
1 Mark
Q6. Dry ice is:
a) Solid water
b) Solid carbon dioxide
c) Liquid nitrogen
d) Frozen carbon monoxide
Answer: b) Solid carbon dioxide
Explanation:
Dry ice is solid CO₂ that sublimes directly to gas without passing through the liquid state. It's called "dry" because it doesn't leave liquid residue.
1 Mark
Q7. The process of change from solid to gas without forming liquid is:
a) Deposition
b) Sublimation
c) Evaporation
d) Condensation
Answer: b) Sublimation
Explanation:
Sublimation is the direct change from solid to gas without passing through the liquid state. Examples: naphthalene balls, dry ice, and camphor.
1 Mark
Q8. Which gas is compressed and supplied to hospitals?
a) Nitrogen
b) Oxygen
c) Helium
d) Argon
Answer: b) Oxygen
Explanation:
Oxygen is essential for respiration and is compressed in cylinders for hospital use. CNG (compressed natural gas) is used as fuel in vehicles.
1 Mark
Q9. The amount of water vapour in air is called:
a) Density
b) Humidity
c) Pressure
d) Temperature
Answer: b) Humidity
Explanation:
Humidity is the amount of water vapour present in air. It affects the rate of evaporation - higher humidity decreases evaporation rate.
1 Mark
Q10. Which fabric is best to wear in summer?
a) Woolen clothes
b) Synthetic clothes
c) Cotton clothes
d) Silk clothes
Answer: c) Cotton clothes
Explanation:
Cotton is a good absorber of water and helps in absorbing sweat, exposing it to the atmosphere for easy evaporation, which causes cooling.
Section B: Short Answer Questions (2 Marks Each) [Total: 20 Marks]
2 Marks
Q11. Why can we smell the aroma of hot food from a distance, but not from cold food?
Answer:
• Hot food particles have more kinetic energy and move faster.
• The rate of diffusion of gas particles increases with temperature.
• Particles spread quickly into the air and reach us from a distance.
• The rate of diffusion of gas particles increases with temperature.
• Particles spread quickly into the air and reach us from a distance.
Explanation:
Temperature increases the kinetic energy of particles, making them move faster and diffuse more rapidly. This is why the smell of hot food reaches us quicker.
2 Marks
Q12. Explain the activity where salt dissolves in water with the help of particle theory.
Answer:
• Salt particles have space between them.
• Water particles also have space between them.
• Salt particles get into the spaces between water particles and spread throughout the water.
• This proves matter is made of particles with spaces between them.
• Water particles also have space between them.
• Salt particles get into the spaces between water particles and spread throughout the water.
• This proves matter is made of particles with spaces between them.
Explanation:
When salt dissolves in water, the water level doesn't increase much, indicating that salt particles fit into the spaces between water molecules, demonstrating that matter is particulate.
2 Marks
Q13. What is diffusion? Give one example.
Answer:
Diffusion is the intermixing of particles of two different types of matter on their own without any external force.
Example: When we put ink drops in water, the ink particles spread throughout the water without stirring, showing diffusion.
Example: When we put ink drops in water, the ink particles spread throughout the water without stirring, showing diffusion.
Explanation:
Diffusion occurs because particles are in constant motion and move into available spaces. Other examples include perfume spreading in air or gases dissolving in water.
2 Marks
Q14. Why is a rubber band still considered a solid even though it can change shape?
Answer:
• A rubber band changes shape when force is applied but returns to its original shape when the force is removed.
• It has a fixed volume.
• The particles maintain their fixed positions despite the shape change.
• It has distinct boundaries.
• It has a fixed volume.
• The particles maintain their fixed positions despite the shape change.
• It has distinct boundaries.
Explanation:
A solid is defined by having a definite volume and maintaining its original state when external force is removed. A rubber band satisfies these conditions.
2 Marks
Q15. Why does a sponge feel soft and can be compressed even though it is a solid?
Answer:
• A sponge has minute holes or pores throughout its structure.
• Air is trapped in these holes.
• When we compress it, the trapped air is expelled out.
• After compression, it regains its original shape, showing it's still a solid.
• Air is trapped in these holes.
• When we compress it, the trapped air is expelled out.
• After compression, it regains its original shape, showing it's still a solid.
Explanation:
The compressibility of a sponge is due to the air pockets, not the solid material itself. The solid matrix of the sponge remains unchanged.
2 Marks
Q16. Define the terms: (a) Boiling (b) Evaporation
Answer:
(a) Boiling: Boiling is a bulk phenomenon where particles from the entire bulk (whole) of the liquid gain enough energy to change into the vapour state at a specific temperature called boiling point.
(b) Evaporation: Evaporation is a surface phenomenon where particles from the surface of the liquid gain enough energy to overcome forces of attraction and change into vapour state at any temperature below boiling point.
(b) Evaporation: Evaporation is a surface phenomenon where particles from the surface of the liquid gain enough energy to overcome forces of attraction and change into vapour state at any temperature below boiling point.
Explanation:
The key difference is that boiling occurs throughout the liquid at a fixed temperature, while evaporation occurs only at the surface at any temperature below the boiling point.
2 Marks
Q17. Why do wet clothes dry faster on a windy day?
Answer:
• Wind carries away the water vapour particles from the clothes.
• This decreases the amount of water vapour in the surrounding air.
• With lower humidity around the clothes, more water particles can escape from the surface.
• This increases the rate of evaporation.
• This decreases the amount of water vapour in the surrounding air.
• With lower humidity around the clothes, more water particles can escape from the surface.
• This increases the rate of evaporation.
Explanation:
Increased wind speed is one of the factors affecting evaporation rate. By removing water vapour, wind creates a lower humidity environment favorable for faster evaporation.
2 Marks
Q18. Convert 25°C to Kelvin scale and 470 K to Celsius scale.
Answer:
To convert °C to K: Add 273
25°C = 25 + 273 = 298 K
To convert K to °C: Subtract 273
470 K = 470 - 273 = 197°C
25°C = 25 + 273 = 298 K
To convert K to °C: Subtract 273
470 K = 470 - 273 = 197°C
Explanation:
The Kelvin scale starts at absolute zero (0 K = -273.15°C). The conversion formula is T(K) = T(°C) + 273.15, or approximately + 273.
2 Marks
Q19. Why do we see water droplets on the outer surface of a glass containing ice-cold water?
Answer:
• The outer surface of the glass becomes very cold.
• Water vapour present in the surrounding air comes in contact with the cold glass surface.
• The water vapour loses energy and changes to liquid water (condensation).
• These liquid water droplets are visible on the outer surface.
• Water vapour present in the surrounding air comes in contact with the cold glass surface.
• The water vapour loses energy and changes to liquid water (condensation).
• These liquid water droplets are visible on the outer surface.
Explanation:
This is a reverse process of evaporation, where water vapour condenses into liquid when cooled, demonstrating that states of matter are interconvertible.
2 Marks
Q20. Why should we apply acetone or perfume on our palm to feel cooling effect?
Answer:
• Acetone and perfume readily evaporate at room temperature.
• The particles of these liquids gain energy from the palm (our body) to overcome forces of attraction.
• This energy absorption from the body causes a cooling sensation.
• This demonstrates that evaporation is an endothermic process that causes cooling.
• The particles of these liquids gain energy from the palm (our body) to overcome forces of attraction.
• This energy absorption from the body causes a cooling sensation.
• This demonstrates that evaporation is an endothermic process that causes cooling.
Explanation:
During evaporation, particles at the surface absorb latent heat of vaporization from the surroundings, making the surroundings cold. This is why our palm feels cool.
Section C: Short Answer Questions (3 Marks Each) [Total: 30 Marks]
3 Marks
Q21. Explain with the help of a diagram why we should spread wet clothes while drying them.
Answer:
When we spread wet clothes:
• The surface area of the clothes exposed to the atmosphere increases.
• With more surface area, more particles can escape from the surface at a time.
• Rate of evaporation directly depends on surface area.
• Therefore, spreading clothes increases the rate of evaporation and they dry faster.
• The surface area of the clothes exposed to the atmosphere increases.
• With more surface area, more particles can escape from the surface at a time.
• Rate of evaporation directly depends on surface area.
• Therefore, spreading clothes increases the rate of evaporation and they dry faster.
Explanation:
Evaporation is a surface phenomenon. More exposed surface means more water molecules can gain enough energy to escape into the gas phase, speeding up the drying process.
3 Marks
Q22. Describe Activity 1.5 and what it demonstrates about particles of matter.
Answer:
In Activity 1.5:
• A crystal of copper sulphate or potassium permanganate is dropped into hot water and cold water separately.
• The solution is not stirred.
• Observation: The colour spreads faster in hot water than in cold water.
This demonstrates:
• Particles of matter are continuously moving.
• Temperature affects the rate of movement of particles.
• Higher temperature = faster movement of particles = faster diffusion.
• A crystal of copper sulphate or potassium permanganate is dropped into hot water and cold water separately.
• The solution is not stirred.
• Observation: The colour spreads faster in hot water than in cold water.
This demonstrates:
• Particles of matter are continuously moving.
• Temperature affects the rate of movement of particles.
• Higher temperature = faster movement of particles = faster diffusion.
Explanation:
The activity clearly shows that kinetic energy of particles increases with temperature, allowing them to mix faster without external disturbance.
3 Marks
Q23. What is latent heat? Define latent heat of fusion and latent heat of vaporization.
Answer:
Latent Heat: Heat energy that is absorbed without showing any rise in temperature is called latent heat (latent means hidden).
Latent Heat of Fusion: The amount of heat energy required to change 1 kg of a solid into liquid at its melting point at atmospheric pressure.
Latent Heat of Vaporization: The amount of heat energy required to change 1 kg of a liquid into gas at its boiling point at atmospheric pressure.
Latent Heat of Fusion: The amount of heat energy required to change 1 kg of a solid into liquid at its melting point at atmospheric pressure.
Latent Heat of Vaporization: The amount of heat energy required to change 1 kg of a liquid into gas at its boiling point at atmospheric pressure.
Explanation:
During phase changes, heat energy goes into breaking intermolecular forces rather than increasing temperature. This is why temperature remains constant during melting or boiling.
3 Marks
Q24. Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer:
• At 273 K, ice contains less energy than water at the same temperature.
• To melt, ice has to absorb latent heat of fusion from the surroundings.
• This large amount of heat energy absorption (about 336,000 J/kg) causes significant cooling of the surroundings.
• Water at the same temperature doesn't undergo any phase change and can only cool through its temperature drop, which is less effective.
• Therefore, ice is more effective for cooling.
• To melt, ice has to absorb latent heat of fusion from the surroundings.
• This large amount of heat energy absorption (about 336,000 J/kg) causes significant cooling of the surroundings.
• Water at the same temperature doesn't undergo any phase change and can only cool through its temperature drop, which is less effective.
• Therefore, ice is more effective for cooling.
Explanation:
The latent heat of fusion is a large amount of energy. Ice melting absorbs this energy from surroundings, causing much more cooling than water simply warming up would cause.
3 Marks
Q25. Explain why we should wear cotton clothes in summer.
Answer:
• During summer, the body produces sweat to maintain temperature (body's cooling mechanism).
• Cotton is a good absorber of water/sweat.
• Cotton absorbs sweat from the body and exposes it to the atmosphere.
• The sweat evaporates from the cotton fabric.
• During evaporation, latent heat of vaporization is absorbed from the body, causing cooling.
• This keeps the body cool and comfortable in summer.
• Cotton is a good absorber of water/sweat.
• Cotton absorbs sweat from the body and exposes it to the atmosphere.
• The sweat evaporates from the cotton fabric.
• During evaporation, latent heat of vaporization is absorbed from the body, causing cooling.
• This keeps the body cool and comfortable in summer.
Explanation:
Cotton facilitates the natural cooling process of the body through perspiration and evaporation. Synthetic materials trap sweat and prevent evaporation, making them unsuitable for summer.
3 Marks
Q26. Describe the characteristics of particles of matter (any three).
Answer:
Three important characteristics of particles of matter are:
1. Space between particles: There is space between particles of matter. Particles of one substance can fit into spaces between particles of another substance, allowing mixing and diffusion.
2. Continuous motion: Particles of matter are always in continuous motion, possessing kinetic energy. This motion increases with increase in temperature.
3. Attractive forces: Particles of matter attract each other with certain forces. The strength of these forces varies between solids, liquids, and gases, being maximum in solids and minimum in gases.
1. Space between particles: There is space between particles of matter. Particles of one substance can fit into spaces between particles of another substance, allowing mixing and diffusion.
2. Continuous motion: Particles of matter are always in continuous motion, possessing kinetic energy. This motion increases with increase in temperature.
3. Attractive forces: Particles of matter attract each other with certain forces. The strength of these forces varies between solids, liquids, and gases, being maximum in solids and minimum in gases.
Explanation:
These characteristics help explain the properties of different states of matter and how substances behave under different conditions of temperature and pressure.
3 Marks
Q27. Why do gases have more pressure than liquids and solids?
Answer:
• In gases, the particles move about randomly at very high speed due to high kinetic energy.
• Due to this random motion, gas particles continuously collide with each other and with the walls of the container.
• Pressure is the force exerted by gas particles per unit area on the walls of the container.
• The large number of collisions with container walls creates significant pressure.
• In liquids and solids, particles have less kinetic energy and move slowly, resulting in fewer and weaker collisions, hence lower pressure.
• Due to this random motion, gas particles continuously collide with each other and with the walls of the container.
• Pressure is the force exerted by gas particles per unit area on the walls of the container.
• The large number of collisions with container walls creates significant pressure.
• In liquids and solids, particles have less kinetic energy and move slowly, resulting in fewer and weaker collisions, hence lower pressure.
Explanation:
Gas pressure is a direct result of molecular collisions. The higher the temperature and the more space available for movement, the greater the pressure.
3 Marks
Q28. Why is steam more dangerous than boiling water?
Answer:
• Steam is water vapour at 373 K (100°C), while boiling water is liquid at the same temperature.
• Steam contains the latent heat of vaporization (about 2,260,000 J/kg for water) in addition to sensible heat.
• When steam comes in contact with skin, it first condenses into water, releasing all its latent heat.
• This large amount of energy release causes severe burns.
• Boiling water only transfers its sensible heat (heat that causes temperature change).
• Therefore, steam causes more severe burns than boiling water at the same temperature.
• Steam contains the latent heat of vaporization (about 2,260,000 J/kg for water) in addition to sensible heat.
• When steam comes in contact with skin, it first condenses into water, releasing all its latent heat.
• This large amount of energy release causes severe burns.
• Boiling water only transfers its sensible heat (heat that causes temperature change).
• Therefore, steam causes more severe burns than boiling water at the same temperature.
Explanation:
The latent heat of vaporization is about 2260 J/g, which is much larger than the sensible heat available in boiling water, making steam significantly more dangerous.
3 Marks
Q29. Explain how a desert cooler works more effectively on a hot dry day.
Answer:
• A desert cooler works by circulating air through wet pads.
• On a hot dry day, humidity is very low.
• The air can hold more water vapour when humidity is low.
• Water from the wet pads evaporates readily in low humidity conditions.
• During evaporation, latent heat is absorbed from the air, cooling it significantly.
• The cooled air is then circulated into the room.
• On a humid day, the air is already saturated with water vapour, so less evaporation occurs and cooling is poor.
• On a hot dry day, humidity is very low.
• The air can hold more water vapour when humidity is low.
• Water from the wet pads evaporates readily in low humidity conditions.
• During evaporation, latent heat is absorbed from the air, cooling it significantly.
• The cooled air is then circulated into the room.
• On a humid day, the air is already saturated with water vapour, so less evaporation occurs and cooling is poor.
Explanation:
Desert coolers are most effective in dry climates where high evaporation rates occur, absorbing maximum latent heat from the surroundings.
3 Marks
Q30. How does pressure affect the state of matter? Explain with an example.
Answer:
• Pressure can change the state of matter by changing the distances between particles.
• Applying pressure brings particles closer together, converting gas to liquid.
• Example: Liquefied Petroleum Gas (LPG) is stored under high pressure in cylinders. At high pressure, gaseous hydrocarbons convert to liquid state, allowing large volumes to be stored in small cylinders.
• Another example: Solid CO₂ (dry ice) is stored under high pressure. When pressure is reduced to 1 atmosphere, it directly sublimes to gas without becoming liquid.
• Thus, temperature AND pressure together determine the state of a substance.
• Applying pressure brings particles closer together, converting gas to liquid.
• Example: Liquefied Petroleum Gas (LPG) is stored under high pressure in cylinders. At high pressure, gaseous hydrocarbons convert to liquid state, allowing large volumes to be stored in small cylinders.
• Another example: Solid CO₂ (dry ice) is stored under high pressure. When pressure is reduced to 1 atmosphere, it directly sublimes to gas without becoming liquid.
• Thus, temperature AND pressure together determine the state of a substance.
Explanation:
Both temperature and pressure affect intermolecular distances and forces, determining which state is stable. This is why phase diagrams show both variables.
Section D: Long Answer Questions (5 Marks Each) [Total: 20 Marks]
5 Marks
Q31. Explain the process of melting and vaporization with reference to kinetic energy, forces of attraction, and latent heat.
Answer:
Melting (Solid to Liquid):
• When heat is applied to a solid, the kinetic energy of particles increases.
• Particles start vibrating with greater speed at their fixed positions.
• The heat energy overcomes the strong forces of attraction between particles.
• Particles leave their fixed positions and start moving more freely.
• At the melting point, the solid converts to liquid state.
• During melting, temperature remains constant because the supplied heat is used to break intermolecular forces (latent heat of fusion).
• For ice: Melting point = 273 K (0°C)
Vaporization (Liquid to Gas):
• When heat is supplied to a liquid, kinetic energy of particles increases.
• Particles start moving faster and with greater energy.
• At the boiling point, particles have enough energy to break free from attractive forces completely.
• The liquid suddenly changes to gas (boiling - bulk phenomenon).
• Below boiling point, only surface particles escape (evaporation - surface phenomenon).
• During vaporization, temperature remains constant as heat energy is absorbed as latent heat of vaporization.
• For water: Boiling point = 373 K (100°C)
Role of Latent Heat:
• Latent heat is the hidden energy absorbed during phase change without temperature rise.
• This energy breaks intermolecular forces, not increasing kinetic energy.
• Latent heat of fusion < Latent heat of vaporization (more energy needed to convert liquid to gas)
• When heat is applied to a solid, the kinetic energy of particles increases.
• Particles start vibrating with greater speed at their fixed positions.
• The heat energy overcomes the strong forces of attraction between particles.
• Particles leave their fixed positions and start moving more freely.
• At the melting point, the solid converts to liquid state.
• During melting, temperature remains constant because the supplied heat is used to break intermolecular forces (latent heat of fusion).
• For ice: Melting point = 273 K (0°C)
Vaporization (Liquid to Gas):
• When heat is supplied to a liquid, kinetic energy of particles increases.
• Particles start moving faster and with greater energy.
• At the boiling point, particles have enough energy to break free from attractive forces completely.
• The liquid suddenly changes to gas (boiling - bulk phenomenon).
• Below boiling point, only surface particles escape (evaporation - surface phenomenon).
• During vaporization, temperature remains constant as heat energy is absorbed as latent heat of vaporization.
• For water: Boiling point = 373 K (100°C)
Role of Latent Heat:
• Latent heat is the hidden energy absorbed during phase change without temperature rise.
• This energy breaks intermolecular forces, not increasing kinetic energy.
• Latent heat of fusion < Latent heat of vaporization (more energy needed to convert liquid to gas)
Explanation:
Both processes involve overcoming intermolecular forces using heat energy. The key insight is that during phase changes, temperature is constant because heat goes into breaking bonds, not increasing molecular motion.
5 Marks
Q32. Compare the properties of solids, liquids, and gases on the basis of: (i) Particle arrangement (ii) Intermolecular forces (iii) Kinetic energy (iv) Compressibility (v) Diffusion
Answer:
Solids:
• Particle arrangement: Highly ordered, tightly packed in fixed positions
• Intermolecular forces: Maximum (strongest)
• Kinetic energy: Minimum (particles vibrate in fixed positions)
• Compressibility: Very low (almost incompressible)
• Diffusion: Negligible
Liquids:
• Particle arrangement: Partially ordered, particles can move within the liquid
• Intermolecular forces: Intermediate (moderate)
• Kinetic energy: Intermediate (particles move freely but within attractions)
• Compressibility: Low (slightly compressible)
• Diffusion: Moderate rate (faster than solids)
Gases:
• Particle arrangement: Random, particles move in all directions with large spaces between them
• Intermolecular forces: Minimum (weakest)
• Kinetic energy: Maximum (particles move very fast)
• Compressibility: Very high (highly compressible)
• Diffusion: Very fast (can diffuse into other gases quickly)
Summary Table:
Property | Solid | Liquid | Gas
---|---|---|---
Shape | Definite | Takes container shape | Takes container shape
Volume | Definite | Definite | Changes with pressure/temperature
Density | High | High | Low
Rigidity | Rigid | Fluid | Highly fluid
Flow | Cannot flow | Can flow | Can flow easily
• Particle arrangement: Highly ordered, tightly packed in fixed positions
• Intermolecular forces: Maximum (strongest)
• Kinetic energy: Minimum (particles vibrate in fixed positions)
• Compressibility: Very low (almost incompressible)
• Diffusion: Negligible
Liquids:
• Particle arrangement: Partially ordered, particles can move within the liquid
• Intermolecular forces: Intermediate (moderate)
• Kinetic energy: Intermediate (particles move freely but within attractions)
• Compressibility: Low (slightly compressible)
• Diffusion: Moderate rate (faster than solids)
Gases:
• Particle arrangement: Random, particles move in all directions with large spaces between them
• Intermolecular forces: Minimum (weakest)
• Kinetic energy: Maximum (particles move very fast)
• Compressibility: Very high (highly compressible)
• Diffusion: Very fast (can diffuse into other gases quickly)
Summary Table:
Property | Solid | Liquid | Gas
---|---|---|---
Shape | Definite | Takes container shape | Takes container shape
Volume | Definite | Definite | Changes with pressure/temperature
Density | High | High | Low
Rigidity | Rigid | Fluid | Highly fluid
Flow | Cannot flow | Can flow | Can flow easily
Explanation:
The differences in macroscopic properties directly arise from the differences in particle-level characteristics like intermolecular forces and kinetic energy.
5 Marks
Q33. Explain the phenomenon of sublimation with the help of Activity 1.13 (Camphor). Also explain deposition.
Answer:
Sublimation (Activity 1.13 - Camphor):
Procedure:
• Take crushed camphor in a china dish
• Place an inverted funnel over it with a cotton plug in the stem
• Heat gently and observe
Observation:
• Camphor gradually disappears without melting into a liquid
• The cotton plug becomes wet (camphor vapours condense on it)
• The smell of camphor spreads in the surroundings
Explanation of Sublimation:
• When camphor is heated, the kinetic energy of particles increases.
• Some particles gain enough energy to directly break free from solid state to gaseous state.
• This direct change from solid to gas WITHOUT passing through liquid state is called SUBLIMATION.
• The energy required for sublimation comes from the heat supplied.
Other examples of sublimation:
• Naphthalene (mothballs) disappears with time
• Dry ice (solid CO₂) sublimes at atmospheric pressure
• Iodine sublimes when heated
Deposition:
• Deposition is the reverse of sublimation.
• It is the direct change from gaseous state to solid state without passing through liquid state.
• Example: When camphor vapours come in contact with the cool cotton plug, they directly convert to solid camphor.
• Another example: Formation of frost on cold glass surfaces (water vapour → ice directly)
• Dry ice formation from CO₂ gas under high pressure is also a form of deposition.
Key Point:
Sublimation and deposition are reverse processes. Both show that states of matter are interconvertible, and a substance need not pass through all states to change from one to another.
Procedure:
• Take crushed camphor in a china dish
• Place an inverted funnel over it with a cotton plug in the stem
• Heat gently and observe
Observation:
• Camphor gradually disappears without melting into a liquid
• The cotton plug becomes wet (camphor vapours condense on it)
• The smell of camphor spreads in the surroundings
Explanation of Sublimation:
• When camphor is heated, the kinetic energy of particles increases.
• Some particles gain enough energy to directly break free from solid state to gaseous state.
• This direct change from solid to gas WITHOUT passing through liquid state is called SUBLIMATION.
• The energy required for sublimation comes from the heat supplied.
Other examples of sublimation:
• Naphthalene (mothballs) disappears with time
• Dry ice (solid CO₂) sublimes at atmospheric pressure
• Iodine sublimes when heated
Deposition:
• Deposition is the reverse of sublimation.
• It is the direct change from gaseous state to solid state without passing through liquid state.
• Example: When camphor vapours come in contact with the cool cotton plug, they directly convert to solid camphor.
• Another example: Formation of frost on cold glass surfaces (water vapour → ice directly)
• Dry ice formation from CO₂ gas under high pressure is also a form of deposition.
Key Point:
Sublimation and deposition are reverse processes. Both show that states of matter are interconvertible, and a substance need not pass through all states to change from one to another.
Explanation:
Sublimation occurs when particles have enough energy to overcome solid-state forces but cooling makes them lose energy rapidly, favoring direct solidification (deposition) rather than intermediate liquid formation.
5 Marks
Q34. Explain the four factors affecting the rate of evaporation with suitable examples.
Answer:
The four factors affecting evaporation rate are:
1. Surface Area:
• Evaporation is a surface phenomenon - only particles at the surface can escape.
• Larger surface area = more particles at surface can escape = higher evaporation rate.
• Example: Clothes dry faster when spread out than when folded. A puddle dries faster than water in a bucket.
2. Temperature:
• Higher temperature increases kinetic energy of particles.
• More particles gain enough energy to escape from the liquid surface.
• Rate of evaporation increases significantly with temperature.
• Example: Water at 50°C evaporates faster than water at 25°C. Wet clothes dry faster on a hot day than on a cold day.
3. Humidity (Amount of water vapour in air):
• Humidity is the amount of water vapour already present in the air.
• If air is already saturated with water vapour, it cannot accept more vapour particles.
• Lower humidity = faster evaporation
• Higher humidity = slower evaporation
• Example: On a humid/rainy day, wet clothes dry slowly. On a dry day, they dry quickly.
4. Wind Speed (Air circulation):
• Moving air (wind) carries away water vapour particles from the surface.
• This reduces the amount of water vapour in the surrounding air (lowers humidity).
• Fresh dry air continuously replaces the vapour-rich air near the surface.
• Higher wind speed = faster evaporation
• Example: Clothes dry much faster on a windy day than on a still day. Hair dries faster with a hair dryer (forced air circulation).
Combined Effect:
• Washing and drying clothes: Spread them (↑ area), in sun (↑ temp), on windy days (↑ wind), away from water sources (↓ humidity) = fastest drying.
1. Surface Area:
• Evaporation is a surface phenomenon - only particles at the surface can escape.
• Larger surface area = more particles at surface can escape = higher evaporation rate.
• Example: Clothes dry faster when spread out than when folded. A puddle dries faster than water in a bucket.
2. Temperature:
• Higher temperature increases kinetic energy of particles.
• More particles gain enough energy to escape from the liquid surface.
• Rate of evaporation increases significantly with temperature.
• Example: Water at 50°C evaporates faster than water at 25°C. Wet clothes dry faster on a hot day than on a cold day.
3. Humidity (Amount of water vapour in air):
• Humidity is the amount of water vapour already present in the air.
• If air is already saturated with water vapour, it cannot accept more vapour particles.
• Lower humidity = faster evaporation
• Higher humidity = slower evaporation
• Example: On a humid/rainy day, wet clothes dry slowly. On a dry day, they dry quickly.
4. Wind Speed (Air circulation):
• Moving air (wind) carries away water vapour particles from the surface.
• This reduces the amount of water vapour in the surrounding air (lowers humidity).
• Fresh dry air continuously replaces the vapour-rich air near the surface.
• Higher wind speed = faster evaporation
• Example: Clothes dry much faster on a windy day than on a still day. Hair dries faster with a hair dryer (forced air circulation).
Combined Effect:
• Washing and drying clothes: Spread them (↑ area), in sun (↑ temp), on windy days (↑ wind), away from water sources (↓ humidity) = fastest drying.
Explanation:
These four factors work together to determine how quickly liquid evaporates. Industrial applications like cooling systems and drying processes use these principles.
