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Q1. Which state of matter shows evaporation?
Evaporation occurs in liquids. It is the process by which a liquid changes into vapour (gas) at any temperature below its boiling point. Evaporation occurs only at the surface of the liquid, making it a surface phenomenon. Solids can sublimate (directly change to gas), but evaporation is specifically a liquid-to-gas change.
Q2. High humidity causes evaporation to
High humidity causes evaporation to decrease. Humidity is the amount of water vapour present in the air. When the air already contains a lot of water vapour, the liquid evaporates more slowly because the air is already saturated with moisture. This is why clothes dry slower in humid weather.
Q3. Solid carbon dioxide is commonly known as
Solid carbon dioxide is commonly known as dry ice. It is called “dry” because it does not melt into a liquid; instead, it directly changes from solid to gas (sublimation). Dry ice is used for cooling purposes and in special effects because it creates a smoky fog when it sublimates.
Q4. Increasing pressure can
Increasing pressure can change the state of matter. By applying high pressure, gases can be liquefied, and sometimes solids can be formed. Pressure, along with temperature, determines the state of a substance. It does not increase temperature directly, destroy matter, or reduce mass.
Q5. During evaporation, only particles at the
During evaporation, only particles at the surface of the liquid escape into the air. Evaporation is a surface phenomenon, meaning it occurs only at the exposed surface of the liquid. Particles below the surface do not have enough energy to escape. This is different from boiling, where bubbles form throughout the liquid.
Q6. Change of state from gas directly to solid is called
The change of state from gas directly to solid is called deposition. This is the reverse of sublimation. In deposition, a gas changes into a solid without passing through the liquid state. Examples include the formation of frost from water vapour on cold surfaces.
Q7. Evaporation differs from boiling because evaporation
Evaporation differs from boiling because evaporation is a surface phenomenon that occurs only at the surface of the liquid at any temperature below the boiling point. Boiling is a bulk phenomenon that occurs throughout the liquid at a specific temperature (the boiling point). Boiling requires heating, while evaporation can occur even without external heating.
Q8. The size of one degree on Celsius scale is
The size of one degree on the Celsius scale is the same as one kelvin on the Kelvin scale. The difference between the two scales is only in their zero points: 0°C = 273.15 K. The degree interval is identical in both scales, meaning a change of 1°C equals a change of 1 K.
Q9. Applying pressure on a gas causes particles to
Applying pressure on a gas causes the particles to come closer. When pressure is applied, the volume decreases, and the particles are pushed closer together. This reduces the spaces between particles. If enough pressure is applied, the gas may liquefy.
Q10. Cooling effect is maximum when evaporation is
The cooling effect is maximum when evaporation is fast. When a liquid evaporates, it absorbs latent heat of vaporisation from its surroundings (including the liquid itself and any surface it is in contact with). This causes cooling. Faster evaporation means more heat is absorbed, resulting in greater cooling.
Q11. Evaporation does NOT require
Evaporation does NOT require heating. Unlike boiling, evaporation can occur at any temperature, even below the boiling point. It does require that the particles have sufficient kinetic energy (which they get from the surroundings), a liquid state, and exposure to the surface. The liquid absorbs heat from its surroundings, but external heating is not necessary.
Q12. Difference in states of matter is due to difference in
The difference in states of matter is due to the difference in the distance between particles. In solids, particles are very close; in liquids, they are a little farther apart; and in gases, they are very far apart. The force of attraction and the arrangement of particles also differ, but the distance between particles is the key difference.
Q13. Which is true about evaporation?
Evaporation absorbs energy from the surroundings. This energy, called latent heat of vaporisation, is used to overcome the forces of attraction between particles and allow them to escape as vapour. This absorption of energy causes cooling, which is why we feel cool when sweat evaporates.
Q14. Evaporation is the change of
Evaporation is the change of state from liquid to gas at any temperature below the boiling point. It is a surface phenomenon and occurs when liquid particles gain enough kinetic energy to escape from the surface into the atmosphere.
Q15. The SI unit of temperature is
The SI unit of temperature is the kelvin (K). The Kelvin scale is used in scientific measurements because it starts at absolute zero (0 K), the lowest possible temperature. Fahrenheit and Celsius are also temperature scales but are not SI units. Joule is the unit of energy.
Q16. Boiling differs from evaporation because boiling
Boiling differs from evaporation because boiling is a bulk phenomenon. In boiling, bubbles of vapour form throughout the entire volume of the liquid, not just at the surface. Boiling occurs at a specific temperature (the boiling point), while evaporation can occur at any temperature.
Q17. To convert Celsius to Kelvin, we add
To convert Celsius to Kelvin, we add 273 (more precisely 273.15). The formula is K = °C + 273.15. For example, 0°C = 273 K. This is because the Kelvin scale starts at absolute zero (-273.15°C), while the Celsius scale starts at the freezing point of water (0°C).
Q18. State of matter depends mainly on
The state of matter depends mainly on temperature and pressure. These two factors determine whether a substance exists as a solid, liquid, or gas. Temperature affects the kinetic energy of particles, while pressure affects the distance between them. Together, they control the state of matter.
Q19. Change of state from solid directly to gas is called
The change of state from solid directly to gas is called sublimation. In sublimation, a solid changes into a gas without passing through the liquid state. Examples include dry ice (solid CO₂) changing into gas and camphor disappearing from solid to vapour.
Q20. Increase in surface area causes evaporation to
An increase in surface area causes evaporation to increase. When the surface area is larger, more particles are exposed to the air, so more particles can escape from the surface. This is why spreading out clothes to dry (increasing surface area) helps them dry faster.
Q21. Pressure and temperature together determine
Pressure and temperature together determine the state of a substance. A substance can be solid, liquid, or gas depending on the combination of temperature and pressure. For example, by applying pressure and reducing temperature, a gas can be converted into a liquid or solid.
Q22. Clothes dry faster on a windy day because
Clothes dry faster on a windy day because the wind carries away the water vapour formed near the surface of the clothes. This reduces the humidity around the clothes, allowing more water to evaporate. Wind also increases the rate of evaporation by constantly bringing drier air to the surface.
Q23. Solid CO₂ changes directly into gas on decreasing pressure because it
Solid CO₂ (dry ice) changes directly into gas when pressure is decreased because it sublimes. At atmospheric pressure, dry ice does not melt into a liquid; it directly turns into carbon dioxide gas. This is why it is called dry ice—it goes from solid to gas without becoming liquid.
Q24. Which condition favours maximum evaporation?
Large surface area favours maximum evaporation. When the surface area is large, more liquid particles are exposed to the air and can escape. High humidity slows evaporation, no wind reduces evaporation, and low temperature reduces the kinetic energy of particles, also slowing evaporation.
Q25. Interconversion of states of matter is possible by changing
Interconversion of states of matter is possible by changing temperature and pressure. By heating or cooling a substance, or by changing the pressure applied to it, we can change it from solid to liquid to gas, or vice versa. The chemical composition remains the same; only the physical state changes.
Q26. Evaporation causes cooling because
Evaporation causes cooling because the evaporating particles absorb energy from the surroundings. To evaporate, the particles need latent heat of vaporisation. They take this energy from the liquid itself and the surrounding surface, which lowers the temperature and causes cooling. This is why sweating cools our bodies.
Q27. Particles escaping during evaporation belong to
Particles escaping during evaporation belong to the highest energy group. Only those particles at the surface that have enough kinetic energy to overcome the forces of attraction can escape into the air. These are the particles with the highest kinetic energy in the liquid.
Q28. Cooling by evaporation is due to
Cooling by evaporation is due to the loss of heat by the surroundings. The evaporating particles take energy from the surroundings, which lowers the temperature of the surroundings. This is a cooling effect. For example, when water evaporates from skin, it takes heat from the body, making us feel cool.
Q29. 0°C is equal to
0°C is equal to 273 K (more precisely 273.15 K). This is the freezing point of water on the Kelvin scale. The Kelvin scale starts at absolute zero (-273.15°C), so 0°C is 273.15 K above absolute zero.
Q30. Evaporation occurs because particles
Evaporation occurs because particles gain energy. They absorb energy from the surroundings, which increases their kinetic energy. When particles have enough kinetic energy, they can overcome the forces of attraction and escape from the liquid surface into the air.
Q31. Which change involves no liquid state?
Sublimation involves no liquid state. In sublimation, a solid changes directly into a gas (or a gas changes directly into a solid) without passing through the liquid state. Melting involves solid to liquid, boiling involves liquid to gas, and freezing involves liquid to solid.
Q32. Increase in temperature affects evaporation by
An increase in temperature affects evaporation by increasing particle motion. Higher temperature means particles have more kinetic energy and move faster. This allows more particles to escape from the surface, increasing the rate of evaporation.
Q33. Sublimation occurs without passing through
Sublimation occurs without passing through the liquid state. It is the direct transition from solid to gas (or gas to solid). The substance skips the liquid phase entirely, which is why it is called sublimation.
Q34. Which factor does NOT affect evaporation?
The colour of liquid does NOT affect evaporation. Evaporation depends on temperature, surface area, humidity, and wind speed. The colour of a liquid does not influence how quickly it evaporates, though it may affect how much heat it absorbs from sunlight (which indirectly affects temperature).
Q35. Applying pressure generally
Applying pressure generally decreases the distance between particles. When pressure is applied, particles are pushed closer together, reducing the spaces between them. This is why gases can be compressed into liquids by applying high pressure.
Q36. Which statement is correct according to the text?
The correct statement is that sublimation skips the liquid state. Sublimation is the process where a solid changes directly into a gas without becoming a liquid. Pressure does affect the state of matter, Kelvin and Celsius degrees are the same size, and evaporation can occur at any temperature below boiling point.
Q37. Dry ice changes directly from solid to gas without becoming
Dry ice changes directly from solid to gas without becoming liquid. This is the process of sublimation. Dry ice (solid CO₂) sublimes at atmospheric pressure, turning directly into carbon dioxide gas without passing through the liquid phase.
Q38. Evaporation is a
Evaporation is a surface phenomenon. It occurs only at the surface of a liquid, where particles with the highest kinetic energy can escape into the air. This is different from boiling, which is a bulk phenomenon occurring throughout the liquid.
Q39. Which state change involves both pressure and temperature?
Change of state involves both pressure and temperature. The state of matter depends on the combination of temperature and pressure. For example, gases can be liquefied by applying high pressure and reducing temperature. All changes of state are influenced by these two factors.
Q40. During evaporation, energy is taken from
During evaporation, energy is taken from the surroundings. The liquid absorbs heat from its environment (including the liquid itself, the container, and the air) to provide the latent heat of vaporisation. This absorption of energy causes cooling in the surroundings.
Q41. Wind speed increases evaporation because it
Wind speed increases evaporation because it removes water vapour from the surroundings. When wind blows, it carries away the water vapour that has just evaporated, reducing the humidity near the liquid’s surface. This creates space for more water to evaporate, speeding up the process.
Q42. Gases can be liquefied by
Gases can be liquefied by applying pressure and reducing temperature. High pressure forces gas particles closer together, and low temperature reduces their kinetic energy. Together, these conditions cause the gas to condense into a liquid. This is how LPG and CNG are stored.
Q43. Evaporation makes surroundings
Evaporation makes surroundings cooler. When a liquid evaporates, it absorbs heat energy from its surroundings. This reduces the temperature of the surroundings, creating a cooling effect. This is why we feel cool when water evaporates from our skin.
Q44. Particles evaporate when they have
Particles evaporate when they have higher kinetic energy. Only particles with enough kinetic energy to overcome the forces of attraction can escape from the liquid surface. These are the fastest-moving particles in the liquid.
Q45. Evaporation proves that particles
Evaporation proves that particles have different kinetic energies. Only the particles with the highest kinetic energy can escape from the liquid surface. The remaining particles have lower kinetic energy, which is why evaporation causes cooling. This shows that not all particles in a liquid have the same energy.
Q46. Which condition reduces evaporation most?
High humidity reduces evaporation the most. When the air already contains a lot of water vapour, there is less room for more vapour. The air near the liquid surface becomes saturated quickly, slowing down the evaporation process. High humidity is the condition that most significantly reduces evaporation.
Q47. Evaporation takes place faster when
Evaporation takes place faster when wind speed is high. Wind removes water vapour from the surface, reducing humidity and allowing more liquid to evaporate. High humidity and small surface area slow evaporation. Covering the liquid prevents evaporation.
Q48. Evaporation occurs
Evaporation occurs at any temperature below the boiling point. It is a continuous process that happens as long as the liquid is exposed to the air. The rate of evaporation increases with temperature but does not require the liquid to reach boiling point.
Q49. Interconversion of states does NOT change
Interconversion of states does NOT change the chemical nature of the substance. The substance remains chemically the same—water is still H₂O whether it is ice, liquid water, or steam. Only the arrangement and energy of particles change, not the chemical composition.
Q50. Humidity refers to
Humidity refers to the amount of water vapour present in the air. It is a measure of how much moisture the air contains. High humidity means the air contains a lot of water vapour, which slows down evaporation. Low humidity means dry air, which allows faster evaporation.