PAGE NO. 3
Q1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Ans. As you know that matter is anything that occupies space and has mass. So, the following things are matter: chair, air, smell, almonds, lemon water and smell of perfume.
Q2. 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.
Ans. The smell of hot sizzling food reaches several meters away, but to get the smell from cold food we have to go close because particles that carry smell of hot food move faster than smell of cold food due to increase in its kinetic energy with the increase in temperature.
Q3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Ans. This shows that particles of water have intermolecular space and has less force of attraction.
Q4. What are the characteristics of the particles of matter?
Ans. Characteristics of particles of matter are:
(a). Particles of matter have space between them.
(b). Particles of matter attract each other.
(c). Particles of matter are continuously moving.
PAGE NO. 6
Q1. 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 chimneys, honey, water, chalk, cotton and iron.
Ans. Air < exhaust from chimney < cotton < water < honey < chalk <iron.
Q2.
(a) Tabulate the difference in characteristics of states of matter.
Ans.
Characteristics | Solid | Liquid | Gases |
Packing of particles | Close packing | Less close packing | Very-very loose |
Spaces between the particles | Very small | Larger than solids; smaller than gases | Very large |
Attractive forces between the particles | Very strong | Less stronger | Very weak |
Motion of particles | Vibratory motion only | Slow particle motion | Rapid movement of particles in all the direction |
volume | definite | definite | Take the volume of the container |
density | Large | Large | Very small |
(b) Comment upon the following:
Rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
RIGIDITY- Rigidity means tendency of matter to maintain its shape when some outside force is applied. Solid have high rigidity due to small interparticle space and strong interparticle force.
COMPRESSIBILITY- It means capability of a substance to decrease its volume when some outside force is applied. Gases possess high compressibility.
FILLING A GAS CONTAINER- The particle of gases can move freely due to large space between the particles and gas fills the container.
FLUIDITY- It means tendency of matter to flow. Gases have the highest fluidity.
SHAPE- Solids have a definite shape whereas liquids and gases take the shape of container.
KINETIC ENERGY- The energy possessed by the particle due to their motion is called kinetic energy.
Q3. Give reason:
(a) A gas fills completely the vessel in which it is kept.
Ans. The molecules of gas can move freely in all directions as they have high kinetic energy and hence fill the vessel completely in which they are kept.
(b) A gas exerts pressure on the walls of the container.
Ans. Due to random motion and kinetic energy the molecules constantly vibrate, move and hit the walls of the container exerting pressure on it.
(c) A wooden table should be called a solid.
Ans. A wooden table should be called a solid because the particles are packed close to each other and cannot be Compressed.
(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.
Ans. It is because molecules of air have less force of attraction between them as compared to solids and particles are highly bound due to this force.
Q4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water Find out why?
Ans. Ice has lower density than water due to its structure. The molecules in ice make a cage like structure with lot of vacant spaces, this makes ice floats on water.
PAGE NO. 9
Q1. Convert the following temperature to Celsius scale:
(a) 300 K
We take 0˚C = 273 K, so to convert the temperature on a kelvin scale to Celsius subtract 273 from given temperature.
300 – 273 = 27˚C
(b) 573 K
573 – 273 = 300˚C
Q2. What is the physical state of water at:
250˚C
Ans. Gas
100˚C
Ans. Liquid as well as gas
Q3. For any substance, why does the temperature remain constant during the change of state?
Ans. The temperature remains constant during the change of state because of heat used to overcome the forces of energy. This is latent heat also called hidden heat.
Q4. Suggest a method to liquefy atmospheric gases.
Ans. Atmospheric gases can be liquified by cooling and applying pressure on them.
PAGE NO. 10
Q1. Why does a desert cooler cool better on a hot dry day?
Ans. Desert cooler cools better on a hot dry day because on a hot day temperature of the atmosphere is high and humidity of air is low which increases the rate of evaporation and thus cause cooling.
Q2. How does the water kept in an earthen pot (MATKA)become cool during summer?
Ans. The earthen pot has lot of pores on it, the water oozes out of these pores and water get evaporate at the surface of the pot which cause cooling effect. This makes the pot cold and water inside the pot cools by the process.
Q3. Why does our palm feel cool when we put some acetone or petrol or perfume on it?
Ans. Our palm feels cool when we put some acetone or petrol or perfume on it because they evaporate when they come in contact of air. The evaporation causes cooling sensation in our hands.
Q4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Ans. Tea in saucer has large surface area than cup. The cooling in saucer takes place faster due to increase in rate of evaporation.
Q5. What type of clothes should we wear in summer?
Ans. We should wear light coloured cotton clothes in summer. Cotton is a good absorber of water and helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.
EXERCISE QUESTIONS
Q1. Convert the following temperatures to the Celsius scale.
(a) 293 K
(b) 470 K
Ans. (a) 293 K
We take 0˚C = 273 K, so to change the temperature on kelvin scale to the Celsius scale subtract 273 from the given temperature.
293 - 273 = 20˚C
(b) 470 K
470 - 273 = 197˚C
Q2. Convert the following temperatures to the kelvin scale.
(a)25˚C
(b) 373˚C
Ans. (a) 25˚C
To convert a temperature to Kelvin add 273 to the given temperature.
273 + 25˚C = 298 K
(b) 373˚C
373 + 273 = 646 K
Q3. 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.
Ans. (a) Naphthalene balls disappear with time without leaving any solid because naphthalene balls directly change into vapours without passing through liquid state.
(b) Perfume change into vapours very fast and due to increase rate of kinetic energy it reaches people sitting several metres away.
Q4. Arrange the following substances in increasing order of forces of attraction between the particles -water, sugar, oxygen.
Ans. Oxygen → water → sugar.
Q5. What is the physical state of water at—
(a) 25˚C
(b) 0˚C
(c) 100˚C?
Ans
(a) At 25˚C water is liquid.
(b) At 0˚C water is solid or liquid.
(c) At 100˚C water is liquid and gas.
Q6. Give two reasons to justify.
(a) Water at room temperature is liquid.
(b) An iron almirah is solid at room temperature.
Ans.
(a) Water at room temperature is liquid because its freezing point is 0˚C and boiling point is 100˚C.
(b) Melting point of iron is higher than room temperature. An iron almirah is rigid and has a fixed shape.so it is solid at room temperature.
Q7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Ans. Ice at 273 K absorbs more heat than water from the substance to overcome the latent heat of fusion hence cooling effect of ice is more than water as water will not gain any extra heat.
Q8. What produces more severe burns, boiling water or steam?
Ans. Steam produce more severe burns because particles in steam have absorbed extra energy in the form of latent heat of vaporisation.
Q9. Name A, B, C, D, E and F in the following diagram showing change in its state.
Ans.
A→ Liquification/melting/fusion
B→ Vaporisation/evaporation
C→ Condensation
D→ Solidification
E→ Sublimation
F→ Sublimation
