Intext Exercise 1
Question 1:
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.
Solution 1:
Matter always occupies some space and mass. It can exist in 3 physical states:
• Solid,
• Liquid and
• Gas.
Matter Reason
Chair, almond Solid state of matter
Cold drink Liquid state of matter
Air, smell of perfume (perfume particles in
air) Gaseous states of matter
Love, hate, cold, smell and thought are sensations, so they are not considered as matter.
Question 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.
Solution 2:
The rate of diffusion increases with increase in temperature due to the increase in the kinetic energy of solid food particles diffused in air. The kinetic energy of hot food particles is high as compared to cold food. Thus, the smell of hot sizzling food reaches us even at a distance, but to get the smell from cold food you have to go close.
Question 3:
A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Solution 3:
One of the characteristics of matter is particles of matter attract each other. The force of attraction between the particles is in the order:
Solid>Liquid> Gas
Thus, liquid particles have less force of attraction between them, so we can cut the force of attraction easily. And there is also space in between the particles of matter. That is why, a diver is able to cut through water in a swimming pool.
Question 4:
What are the characteristics of particles of matter?
Solution 4:
Any matter has some characteristics like:
(i) Particles of matter have space between them. (ii) Particles of matter are continuously moving. (iii) Particles of mater attract each other.
Intext Exercise 2
Question 1:
The 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.
Solution 1:
The order of increasing density of the given matters is:
Air < Exhaust from chimney < Cotton < Water < Honey < Chalk < Iron
Question 2:
(a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.
Solution 2:
(a) The differences in the characteristics of states of matter:
S. No. Solid state Liquid state Gaseous state
1. It has definite shape and
volume. It has no definite shape, but
has definite volume.
Liquids attain the shape of the vessel in which they are kept. It neither has a definite
shape nor a definite volume.
2. It is incompressible It is compressible to a small
extent. It is highly
compressible.
3. The force of attraction between the particles of solids is highest. The force of attraction between liquid particles is less than solid particles but greater than gas particles. The force of attraction between the gaseous particles is least.
5. Particles of solid cannot
move freely. Liquid particles move
freely. Gaseous particles are in
a continuous and random motion.
(b) Rigidity: The tendency of matter to resist a change in shape.
Compressibility: The ability to reduce in volume when force is applied.
Fluidity: It is the ability of matter to flow. Only liquid and gases can flow and are called fluid.
Filling a gas container: Gases do not have definite shape and volume. Gases take the shape of the container in which filled. By filling a gas container, it means the attainment of shape of the container by the gas.
Shape: It means a definite boundary. Only solids have definite volume. Kinetic energy: The energy possessed by a particle due to its motion. Density: Mass per unit volume.
Question 3:
Give reasons:
(a) A gas fills completely the vessel in which it is kept. (b) A gas exerts pressure on the walls of the container. (c) A wooden table should be called 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.
Solution 3:
(a) The gas particles move freely in all directions due to less force of attraction between the particles. Gas takes the shape of the container in which it is kept. Therefore, gas completely fills the vessel.
(b) The gas particles move freely in all directions due to less force of attraction between the particles. These gaseous particles continuously collide among themselves and they also hit the walls of the container with a greater force. Pressure is defined as the force exerted by the gas particles per unit area. Thus, gas exerts pressure on the walls of the container.
(c) A wooden table has a definite shape and volume. It is very rigid and its shape cannot be changed easily i.e., it has the characteristics of a solid. Hence, a wooden table should be considered as a solid.
(d) Air particles have large space in between them due to the least force of attraction between the particles. Whereas, wood has little space between the particles due to high force of attraction between the particles. Wood is rigid. For this reason, we can easily move our hands in air, but to do the same through a solid block of wood, we need a karate expert.
Question 4:
Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Solution 4:
Density is mass per unit volume of a substance.
As the volume of a substance increases, its density decreases.
Though ice is a solid, it has large number of empty spaces in its structure.
These empty spaces are larger as compared to the spaces present between the particles of water. For this reason, the volume of ice is greater than that of water. Higher the volume, lesser will be the density. Hence, the density of ice is less than that of water.
Intext Exercise 3
Question 1:
Convert the following temperature to Celsius scale: (a) 300 K
(b) 573 K
Solution 1:
X °C = (X + 273) K
(a) 300 K = (300 −273) °C = 27°C (b) 573 K = (573 −273) °C= 300°C
Question 2:
What is the physical state of water at: (a) 250°C
(b) 100°C
Solution 2:
(a) Boiling point of water = 100°C, above this temperature water exists in gaseous state. Thus, water at 250°C exists in gaseous state.
(b) At 100°C, water exists in both liquid and gaseous states.
Question 3:
For any substance, why does the temperature remain constant during the change of state?
Solution 3:
During a change of state, the temperature remains constant. This is because all the heat supplied to increase the temperature, is utilised to supply latent heat of vapourisation which does not contribute to increase the temperature of the substance.
Question 4:
Suggest a method to liquefy atmospheric gases.
Solution 4:
Atmospheric gases can be liquefied by applying pressure and reducing the temperature. Intext Exercise 4
Question 1:
Why does a desert cooler cool better on a hot dry day?
Solution 1:
During evaporation, the liquid particles absorb energy from the surroundings which causes the cooling effect. The rate of evaporation depends on the amount of water vapour present in air or humidity. If the amount of water vapour present in air is less, then rate of evaporation will be more. On a hot dry day, the amount of water vapour present in air is less. Thus, water present inside the desert cooler evaporates rapidly, and it cools the surroundings more easily. Therefore, a desert cooler cools better on a hot dry day.
Question 2:
How does water kept in an earthen pot (matka) become cool during summers?
Solution 2:
An earthen pot consists of many tiny pores through which the liquid inside the pot
evaporates. That makes the water inside the pot cool. In this way, water kept in an earthen pot became cool during summers.
Question 3:
Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Solution 3:
Organic compounds like acetone or petrol or perfume are volatile in nature. When we put some acetone or petrol or perfume on our palm, it evaporates. During evaporation, particles of these organic liquids absorb energy from the surroundings or the surface of the palm
making the surroundings or surface of the palm cool. Hence, our palm feels cold when we put some acetone or petrol or perfume on it.
Question 4:
Why are we able to sip hot tea or milk faster from a saucer than a cup?
Solution 4:
Hot tea or milk has a larger surface area in a saucer than in a cup. Rate of evaporation is faster in case of greater surface area. Thus, the liquid cools faster in a saucer than in a cup. For this reason, we are able to sip hot tea or milk faster from a saucer than a cup.
Question 5:
What type of clothes should we wear in summers?
Solution 5:
In summer, we should wear cotton clothes because cotton clothes can absorb more sweat from our body and exposes the liquid to the atmosphere, making evaporation faster. During this evaporation, particles on the surface of the liquid gain energy from our body surface, making the body cool.
NCERT Exercise
Question 1:
Convert the following temperatures to Celsius scale. (a) 300 K
(b) 573 K Solution 1: K= – 273°C
(a) 300 K = (300 − 273) °C = 27 °C
(b) 573 K = (573 − 273) °C = 300 °C
Question 2:
Convert the following temperatures to Kelvin scale. (a) 25°C
(b) 373°C
Solution 2:
0°C = 273 K
(a) 25 °C = (25 + 273) K = 298 K (b) 373°C = (373 + 273) K= 646 K
Question 3:
Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid. (b) We can get the smell of perfume sitting several metres away. Solution 3:
(a) Few substances undergo sublimation easily at room temperature. Such as naphthalene balls changes state from solid to gas takes place easily. Thus, naphthalene balls disappear with time without leaving any solid.
(b) Gaseous particles possess high kinetic energy. Particles of perfume diffuse into these gaseous particles at a very faster rate and reach to our nose. This enables us to smell the perfume from a distance.
Question 4:
Arrange the following substances in increasing order of forces of attraction between particles
− water, sugar, oxygen.
Solution 4:
The increasing order of forces of attraction between particles of matter is: Solid>Liquid>Gas
Water = Liquid, Sugar = Solid, Oxygen = Gas.
Thus, the increasing order of forces of attraction between the particles of water, sugar and oxygen is
Oxygen < Water < Sugar
Question 5:
What is the physical state of water at: (a) 25°C
(b) 0°C
(c) 100°C
Solution 5:
(a) Melting point of water = 0°C
At 25°C, water exists in the liquid state.
(b) At 0 °C, water can exist as both solid and liquid. At this temperature, ice starts changing into its liquid form i.e., water.
(c) Boiling point of water =100 °C. At 100 °C, water can exist as both liquid and gas. At this temperature, water starts changing from its liquid state to its gaseous state, i.e., water vapours/steam.
Question 6:
Give two reasons to justify:
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
Solution 6:
(a) At room temperature (25 °C), water is a liquid due to few characteristics of liquid, such as:
(i) Water has no shape but has a fixed volume. It takes the shape of the container in which it is kept.
(ii) Water can flow.
(b) An iron almirah is a solid at room temperature (25 °C) due to few characteristics of solid: (i) it has a definite shape and volume like a solid.
(ii) it is rigid as solid.
Question 7:
Why is ice at 273 K more effective in cooling than water at the same temperature?
Solution 7:
Both ice and water are at same temperature 273 K. But ice at 273 K has less energy than
water because water possesses the additional energy of latent heat of fusion. Hence, at 273 K, ice is more effective in cooling than water.
Question 8:
What produces more severe burns, boiling water or steam?
Solution 8:
Both steam and water are at same temperature 373 K. But steam has more energy than boiling water because it possesses the additional energy of latent heat of vapourisation. Therefore, steam produces more severe burns than boiling water.
Question 9:
Name A, B, C, D, E and F in the following diagram showing change in its state.
