NCERT Page no. 3
Q: 1. Which of the following are matters ? chair, air, love, smell, hate, almond, thought, cold, lemon, water, smell of perfume.
Answer: chair, air, smell, almonds, cold, lemon, water, smell of perfume, all these are matters as these have volume and mass.
(Love, hate, thought, cold these are not having any mass and these also do not occupy space so these are not matters.)
Q: 2. Give reasons for the following observations: The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
Answer: As the particles of hot food have more kinetic energy so the smell of hot sizzling food reaches several meters away. The rate of diffusion is more of hot food than the particles of the cold foods. So to get smell of cold foods we have to go close.
Q: 3. The diver is able to cut through water in a swimming pool. Which property of matter does this observation show ?
Answer: As the diver is able to cut through water in swimming pool this shows that:
1.Water have large intermolecular space.
2. Their molecules are less tightly bound together. (There is less force of attraction between molecules.)
Q: 4. What are the characteristics of particle of matters ?
Answer: All matters are composed of particles and particles have some properties:
1. Matters consists of tiny particles which can not be seen with naked eyes.
2. These particles have space between them.
3. Particles attracts each others due to intermolecular force of attraction.
4. Particles are always in motion. i.e. they have kinetic energy.
5. Kinetic energy increases with increase in temperature.
6. Intermolecular force increases with decrease in space between these and vice versa.
NCERT Page no. 6
Q. 1. Mass per unit volume of a substance is called density, (density= mass/volume). Arrange the following in order of increasing density. Air, exhaust from chimney, honey, water, chalk, cotton and iron.
Answer: increasing density: air< exhaust from chimney< cotton< water< honey< chalk< iron.
Q. 2. a) Tabulate the difference in the characteristics of the states of matter:
Answer:
| Characteristic | Solid | Liquid | Gas |
| Shape | Fixed Shape | No Fixed Shape | No Fixed Shape |
| Rigidity | Rigid | Not Rigid | Not Rigid |
| Volume | Fixed Volume | Fixed Volume | No Fixed Volume |
| Compressibility | Negligible | Compressible | Highly Compressible |
| Intermolecular Force | Maximum | Less than solid | Very less |
| Intermolecular Space | Very Less | More than solid | Maximum |
Q. 2. b) Comment upon the following: Rigidity, Compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.
Answer:
Rigidity: The tendency of a substance to maintain its shape when a outside force is applied on it.
Compressiblity: when external force is applied on a matter this force can bring their particles close to each other. This property is called compressibility. Gases and liquids are compressible but solids are not.
Fluidity: It is the tendency of particles of a matter to flow. Gases and liquids have fluidity.
Filling a gas container: Gas particles vibrate randomly in all directions and gas can fill the container.
Shape: Solid have definite shape as they have intramolecular force. Liquid and gas have no definite shape they attain the shape of the container.
Kinetic Energy: The energy possessed by particles due to their motion is called kinetic energy. Gas have maximum kinetic energy so their molecules vibrate randomly.
Density: It is mass per unit volume. D= Mass/ Volume. Increasing density Gas> Liquids> Solids.
Q: 3. Give reasons:
a) A gas fills completely the vessels in which it is kept.
Reason: As the gas molecules have high kinetic energy so they keep moving in all direction in a vessels. So gas fills the container completely.
b) A gas exerts pressure on the walls of the container.
Reason: The gas molecules have high kinetic energy so they are in constant motion. These molecules vibrate, move, and hit the walls of the container thereby exerting pressure on the walls of container.
c) A wooden table should be called a solid.
Reasons: It can not be compressed, can not flow, have definite shape, particles are tightly packed. Due to all these characteristics wooden table should be called a solid.
d) we can easily move our hand in air but to do the same through a solid blocks of wood we need a karate expert.
Reason: It is because air molecules has force of attraction between them so very less force is required to separate them and pass through it. But solid molecules are tightly bound due to large force of attraction so large amount of external force is required to pas through solid.
Q. 4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why ?
Reason: For a given mass of water, volume of ice is greater then that of water so the density of water is more then ice. Though ice is solid it has cage like structure, there is large space between particles hence ice density is less then water. so substance with less density then water, floats on water.
NCERT Page No. 9
Q. 1. Convert the following temperature to Celsius scale:
a) 300 K b) 573 K
Answer: a) 300-273= 27ᵒ C
b) 573-273= 300ᵒ C
Q.2. What is the physical state of water at:
a) 25ᵒ C b) 100ᵒ C
Answer: a) at 25ᵒ C = Gas, b) at 100ᵒ C = Liquid as well as gas.
Q. 3. For any substance, why does the temperature remain constant during the change of state ?
Answer: As the heat supplied to increase the temperature of the substance is used up to transform the state of matter of the substance. The molecules of this matter use heat to overcome the force of attraction between the particles. so at the time of change of state temperature remain constant.
Q. 4. Suggest a method to liquify atmospheric gases ?
Answer: By applying high pressure on gas it can be liquified. for this atmospheric gases are taken in a cylinder with piston on it and by cooling and applying pressure on them gas can be liquefied.
NCERT Page No. 10
Q. 1. Why does a desert cooler cool better on a hot dry day ?
Answer: It is because there is high temperature and hot dry air (less humid) which cause better evaporation. Hence more evaporation will cause more cooling effect.
Q. 2. How does the water kept in an earthen pot (matka) become cool during summer ?
Answer: The earthen pot is porous, it has lot of pores on its surface. The water oozes out through these pores and gets evaporated from the surface of pot thereby causes cooling effect. This makes the pot and water in it cold.
Q. 3. Why does our palm feels cold when we put some acetone or petrol or perfume on it ?
Answer: Acetone, petrol or perfume evaporates quickly (they are volatile) when they come in contact with air. Evaporation is facilitated as it uses from our palms hence leaving a cooling sensation on our hands.
Q. 4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup ?
Answer: Tea in a saucer has a large surface area then in a cup, so evaporation is faster with increased surface area. The cooling of tea in a saucer takes place sooner than in the cup hence we are able to sip for tea or milk from saucer rather than a cup.
Q. 5. What types of clothes should we wear in summer ?
Answer: In summer you should wear light colored cotton clothes. Light color reflects heat. Cotton clothes has pores in it which absorbs sweat and facilitate sweat to evaporate faster thereby giving cooling effect to our skin.
Exercise questions from NCERT
Q. 1. Convert the following temperatures to the Celsius scale: a) 293 Kelvin, b) 470 Kelvin
Answer: a) 293 – 273 = 20ᵒ C b) 470 – 273 = 197ᵒ C
Q. 2. Convert the following temperatures to the Kelvin scale a) 25ᵒ C b) 373ᵒ C
Answer: a) 25 + 273 = 298 K b) 373 + 273 = 646 K
Q. 3. You reason for the following observation……
a) Naphthalene bolls disappear with time without leaving any solid.
Answer: Naphthalene can sublime and directly change into vapor state without leaving any solid. So naphthalene bolls disappear with time without leaving any solid. This is due to sublimation.
b) We can get the smell of perfume sitting several meters away.
Answer: This is due to because perfume contain volatile solvent which can diffuse faster in air and can reach people sitting several meters away.
Q. 4 Arrange the following substances in increasing orders of force of attraction between the particles- water, sugar, oxygen.
Answer: Increasing orders of increase in force of attraction between particles… Oxygen > Water > Sugar.
Q. 5. What is the physical state of water at- a) 25ᵒ C b) 0ᵒ C c) 100ᵒ C.
Answer: a) at 25ᵒ C water is liquid (room temperature)
b) at 0ᵒ C water is at freezing point, hence both solid and liquid phase is found.
c) at 100ᵒ C water is at boiling point, hence both liquid and gas phase is found.
Q. 6. Give two reasons to justify:
a) Water at room temperature is liquid.
Answer: Water is liquid at room temperature because its freezing point is lower than room temperature and boiling point is higher than room temperature.
b) An iron almirah is solid at room temperature.
Answer: Melting and boiling point of iron is more then room temperature. So iron almirah is solid at room temperature.
Q. 7. Why is ice at 273 K more effective in cooling than water at the same temperature ?
Answer: At 273 K, ice has less energy than water. Water possesses additional latent heat of fusion. Hence, at 273 K ice is more effective in cooling than water.
Q. 8. What produces more severe burns, boiling water or steam ?
Answer: Steam at 100ᵒ C produce more heat because extra heat is hidden in steam called latent heat of vaporization where as this heat is not hidden in boiling water. therefore, burns produced by steam are more severe than those produced by boiling water.
Q. 9. Name A, B, C, D, E and F in the following diagram showing change in its state.
Answer:
Answer: A- Solid to Liquid is Melting/ Fusion/ Liquefaction
B- Liquid to Gas is Evaporation / Vaporization
C- Gas to Liquid is Condensation
D- Liquid to Solid is Solidification
E- Solid to Gas is Sublimation
F- Gas to Solid is Sublimation
