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Page No: 03 questions
1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume
✅ Matter: Chair, air, almonds, lemon water
❌ Not Matter: Love, smell, hate, thought, cold, smell of perfume
Answer:
Only those things which have mass and occupy space are considered matter. So, chair, air, almonds, and lemon water are matter. Love, hate, thought, smell, cold, and smell of perfume are feelings or sensations, not matter.
2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Answer:
This happens because particles of matter are continuously moving and they diffuse.
When food is hot, the kinetic energy of its particles is higher, so the particles move faster and diffuse more rapidly into the air.
In cold food, diffusion is slower, so you need to get closer to smell it.
3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Answer:
This shows that particles of matter have space between them.
Water particles are not tightly packed, so the diver can easily pass through by pushing the particles aside.
4. What are the characteristics of the particles of matter?
Answer: The main characteristics of the particles of matter are:
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Particles of matter have space between them.
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Particles of matter are continuously moving.
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Particles of matter attract each other.
Page No:- 06
1. The mass per unit volume of a substance is called density. (Density = Mass/Volume)
Arrange the following in order of increasing density –
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Air
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Exhaust from chimneys
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Honey
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Water
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Chalk
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Cotton
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Iron
Answer: The substances arranged in order of increasing density are:
Air < Exhaust from chimneys < Cotton < Water < Honey < Chalk < Iron
2. (a) Tabulate the differences in the characteristics of states of matter.
| Characteristic | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Definite shape | Takes shape of the container | No definite shape |
| Volume | Fixed volume | Fixed volume | No fixed volume |
| Compressibility | Very low | Low | High |
| Fluidity | Rigid, not fluid | Fluid, can flow | Highly fluid, can flow easily |
| Kinetic Energy | Low | Higher than solids | Highest |
| Density | High | Lower than solids | Very low |
(b) Comment upon the following:
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Rigidity: Solids are rigid, meaning they maintain their shape, while liquids and gases are not rigid.
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Compressibility: Gases are highly compressible, liquids are slightly compressible, and solids are not compressible.
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Fluidity: Liquids and gases are fluids and can flow. Solids do not flow and are not considered fluids.
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Filling a gas container: A gas fills the entire container because the particles are far apart and move freely.
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Shape: Solids have a definite shape, liquids take the shape of the container, and gases have no fixed shape.
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Kinetic Energy: The kinetic energy of particles increases from solids to liquids to gases.
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Density: Solids generally have higher density compared to liquids and gases, except for ice (which has lower density than water).
3. Give reasons:
(a) A gas fills completely the vessel in which it is kept.
Answer: Gases have no fixed shape or volume. The particles are far apart and move freely, spreading out to fill the entire container.
(b) A gas exerts pressure on the walls of the container.
Answer: Gas particles move randomly at high speeds and collide with the walls of the container, creating pressure.
(c) A wooden table should be called a solid.
Answer: A wooden table has a fixed shape, volume, and rigid structure, making it a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
Answer: Air is a gas with particles far apart, allowing easy movement. Solid wood has tightly packed particles that resist movement, requiring more force.
4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Answer: Ice has a lower density than water because its particles are arranged in a crystalline structure with more space between them. This causes ice to float on water, as objects with lower density float on liquids with higher density.
Page No:- 09
1. Convert the following temperature to Celsius scale:
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a. 300 K
Answer:
To convert from Kelvin to Celsius:
So,
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b. 573 K
Answer:
So,
2. What is the physical state of water at:
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a. 250ºC
Answer:
At 250ºC, water is in the gaseous state because water boils at 100ºC under normal atmospheric pressure, so at 250ºC, it will be steam or vapor. -
b. 100ºC
Answer:
At 100ºC, water is at its boiling point under normal atmospheric pressure. It can exist in both liquid and gaseous states, depending on whether it is boiling or not.
3. For any substance, why does the temperature remain constant during the change of state?
Answer:
During the change of state, the temperature remains constant because the heat energy supplied is used to overcome the forces of attraction between the particles, not to increase their kinetic energy. This energy is called latent heat. For example, during melting or boiling, the temperature does not rise until all the substance has changed state.
4. Suggest a method to liquefy atmospheric gases.
Answer:
To liquefy atmospheric gases, we can increase the pressure and decrease the temperature. By applying high pressure and low temperatures, gases are compressed and their particles come closer, leading to condensation. For example, liquefied oxygen and liquefied nitrogen are obtained by compressing and cooling air.
page no- 10
Questions and Answers:
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Why does a desert cooler cool better on a hot dry day?
Answer: A desert cooler works better on a hot dry day because of the high rate of evaporation. When the air is dry, it can absorb more water vapor, which enhances the cooling effect. The desert cooler uses water to evaporate, and the evaporation absorbs heat from the surrounding air, thus cooling it down. The more moisture the air can absorb, the more effective the cooling process.
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How does the water kept in an earthen pot (matka) become cool during summer?
Answer: Water kept in an earthen pot becomes cool during summer due to the porosity of the material. The water inside the pot gradually seeps out through the tiny pores in the clay, and as it evaporates, it absorbs heat from the surroundings, cooling the water inside the pot. This cooling effect is enhanced due to evaporation from the surface of the pot.
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Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer: Our palm feels cold when we put acetone, petrol, or perfume on it because these liquids evaporate quickly. During evaporation, the particles of these liquids absorb heat from the surface of the skin (in this case, our palm), which lowers the temperature of the skin, making it feel cold. This is due to the latent heat of vaporization required for the evaporation process.
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Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer: We are able to sip hot tea or milk faster from a saucer because the surface area of the liquid exposed to the air is much larger in the saucer than in a cup. A larger surface area allows for faster evaporation of the hot liquid, which cools the liquid more quickly, making it easier to drink. The evaporation process helps in reducing the temperature of the liquid, making it more comfortable to sip.
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What type of clothes should we wear in summer?
Answer: In summer, we should wear light, loose-fitting, and breathable clothes made from cotton or linen. These fabrics allow air to pass through and help sweat evaporate easily, which keeps the body cool. Cotton is particularly effective because it absorbs sweat and facilitates evaporation, which is crucial for cooling the body during hot weather.
Exercises
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Convert the following temperatures to the Celsius scale:
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(a) 293 K
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(b) 470 K
Answer:
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(a) To convert from Kelvin to Celsius, subtract 273 from the Kelvin temperature.
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(b)
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Convert the following temperatures to the Kelvin scale:
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(a) 25°C
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(b) 373°C
Answer:
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(a) To convert from Celsius to Kelvin, add 273 to the Celsius temperature.
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(b)
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Give reasons for the following observations:
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(a) Naphthalene balls disappear with time without leaving any solid.
Answer: Naphthalene undergoes sublimation, a process where it changes directly from solid to gas without passing through the liquid state. -
(b) We can get the smell of perfume sitting several meters away.
Answer: Perfume molecules evaporate and diffuse in the air, allowing their scent to travel and be detected from a distance.
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Arrange the following substances in increasing order of forces of attraction between the particles—water, sugar, oxygen.
Answer: Oxygen (weakest) < Water < Sugar (strongest).
(In gases like oxygen, the particles are far apart, leading to weak forces of attraction. In liquids like water, particles are closer, leading to moderate forces. In solids like sugar, particles are tightly packed, leading to the strongest forces.) -
What is the physical state of water at:
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(a) 25°C
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(b) 0°C
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(c) 100°C
Answer:
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(a) Liquid
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(b) Solid (Ice)
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(c) Gas (Steam)
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Give two reasons to justify:
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(a) Water at room temperature is a liquid.
Answer: Water has a melting point of 0°C and a boiling point of 100°C, and at room temperature (around 25°C), it remains in the liquid state. -
(b) An iron almirah is a solid at room temperature.
Answer: Iron has a high melting point (about 1538°C), and at room temperature, it remains in the solid state due to the strong forces of attraction between its particles.
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Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer: Ice at 273 K absorbs latent heat of fusion while melting, which requires energy without changing its temperature. This process makes ice more effective in cooling than water, as it absorbs more heat from the surroundings.
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What produces more severe burns, boiling water or steam?
Answer: Steam produces more severe burns than boiling water because steam contains more energy (latent heat of vaporization) and can release that energy upon condensation, causing more damage.
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Name A, B, C, D, E, and F in the following diagram showing change in its state.
Answer: This diagram shows the changes of state between solids, liquids, and gases, along with the effects of temperature and pressure. The labels A to F represent specific phase changes. Here's what each label corresponds to:
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A: Melting – Solid to Liquid
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B: Evaporation/Boiling – Liquid to Gas
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C: Condensation – Gas to Liquid
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D: Freezing – Liquid to Solid
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E: Sublimation – Solid to Gas
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F: Deposition – Gas to Solid
The directions at the top and bottom indicate:
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Increase heat and decrease pressure → favors Gas phase
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Decrease heat and increase pressure → favors Solid phase
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