Question 1

Q1: Convert the following temperatures to the celsius scale. (a) 293 K (b) 470 K

Accepted Answer

Given: Temperatures in Kelvin scale: (a) 293 K (b) 470 K To Find: Convert the given temperatures to the Celsius scale. Formula: The relationship between Kelvin (K) and Celsius ($^{\circ}\mathrm{C}$) scales is: Temperature in $^{\circ}\mathrm{C}$ = Temperature in K - 273 Solution: (a) 293 K Temperatu...

Question 2

Q2: Convert the following temperatures to the kelvin scale. (a) $25^{\circ} \mathrm{C}$ (b) $373^{\circ} \mathrm{C}$

Accepted Answer

Given: Temperatures in Celsius scale: (a) $25^{\circ} \mathrm{C}$ (b) $373^{\circ} \mathrm{C}$ To Find: Convert the given temperatures to the Kelvin scale. Formula: The relationship between Celsius ($^{\circ}\mathrm{C}$) and Kelvin (K) scales is: Temperature in K = Temperature in $^{\circ}\mathrm{C}...

Question 3

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 s...

Accepted Answer

Answer: (a) Naphthalene balls disappear with time without leaving any solid. Reason: Naphthalene balls undergo a process called sublimation. Sublimation is the direct conversion of a substance from the solid state to the gaseous state without passing through the liquid state. The solid naphthalene s...

Question 4

Q4: Arrange the following substances in increasing order of forces of attraction between the particles- water, sugar, oxygen.

Accepted Answer

Answer: The force of attraction between particles depends on the state of matter. The forces are weakest in gases, stronger in liquids, and strongest in solids. 1.  Oxygen: It is a gas at room temperature. The forces of attraction between its particles are very weak (negligible). 2.  Water: It is a...

Question 5

Q5: What is the physical state of water at- (a) $25^{\circ} \mathrm{C}$ (b) $0^{\circ} \mathrm{C}$ (c) $100^{\circ} \mathrm{C}$ ?

Accepted Answer

Answer: The freezing point of water is $0^{\circ} \mathrm{C}$ and the boiling point is $100^{\circ} \mathrm{C}$ (at 1 atm pressure). (a) At $25^{\circ} \mathrm{C}$: This temperature is between the freezing point and the boiling point of water. Therefore, at $25^{\circ} \mathrm{C}$, water is in the l...

Question 6

Q6: Give two reasons to justify- (a) water at room temperature is a liquid. (b) an iron almirah is a solid at room temperature.

Accepted Answer

Answer: (a) Water at room temperature is a liquid. Justification: 1.  No Fixed Shape, Fixed Volume: Water does not have a fixed shape and takes the shape of the container it is poured into. However, it has a fixed volume. These are characteristic properties of a liquid. 2.  Fluidity: Water can flow...

Question 7

Q7: Why is ice at 273 K more effective in cooling than water at the same temperature?

Accepted Answer

Reason: Ice at 273 K ($0^{\circ} \mathrm{C}$) is more effective in cooling than water at 273 K ($0^{\circ} \mathrm{C}$) because it can absorb more heat. When ice at 273 K is used for cooling, it absorbs heat from the surroundings in two stages: 1.  Latent Heat of Fusion: First, the ice absorbs heat...

Question 8

Q8: What produces more severe burns, boiling water or steam?

Accepted Answer

Answer: Steam produces more severe burns than boiling water, even though both are at the same temperature ($100^{\circ} \mathrm{C}$ or 373 K). Reason: This is because particles in steam have more energy than particles in boiling water at the same temperature. 1.  Boiling Water: Boiling water at $100...

Question 9

Q9: Name A, B, C, D, E and F in the following diagram showing change in its state

Accepted Answer

Answer: The diagram shows the interconversion between the three states of matter: solid, liquid, and gas. The processes are identified as follows:    A (Solid to Liquid): This process is called Melting or Fusion.    B (Liquid to Gas): This process is called Vaporization or Boiling.    C (Gas to Liqu...

Question 10

Q1: Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.

Accepted Answer

Answer: Matter is defined as anything that has mass and occupies space. Based on this definition: Matter:    Chair: It has mass and occupies space.    Air: It is a mixture of gases, has mass, and occupies space.    Almonds: They have mass and occupy space.    Lemon water: It is a liquid mixture that...

Question 11

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 ha...

Accepted Answer

Reason: The phenomenon described is due to the process of diffusion, which is dependent on the kinetic energy of particles. 1.  Kinetic Energy: Particles of matter are in continuous motion and possess kinetic energy. The kinetic energy of particles increases with an increase in temperature. 2.  Hot...

Question 12

Q3: A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Accepted Answer

Answer: This observation demonstrates two important properties of the particles of matter (in this case, water): 1.  Particles of matter have space between them: The particles in a liquid are not tightly packed. There are intermolecular spaces between the water molecules. These spaces allow the dive...

Question 13

Q4: What are the characteristics of the particles of matter?

Accepted Answer

Answer: The main characteristics of the particles of matter are as follows: 1.  Matter is made up of very small particles: These particles are too small to be seen with the naked eye. For example, a single crystal of potassium permanganate contains millions of tiny particles. 2.  Particles of matter...

Question 14

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...

Accepted Answer

Answer: Density is a measure of how tightly packed the matter in a substance is. Generally, gases are the least dense, followed by liquids, and then solids are the most dense. We can arrange the given substances based on this principle.    Gases: Air, Exhaust from chimneys. Exhaust from chimneys con...

Question 15

Q2: (a) Tabulate the differences in the characterisitcs of states of matter. (b) Comment upon the following: rigidity, compressibility, fluidity, filling...

Accepted Answer

Answer: (a) Differences in the characteristics of states of matter: | Characteristic            | Solids                                       | Liquids                                           | Gases                                               | |---------------------------|--------------------...

Question 16

Q3: 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 sh...

Accepted Answer

Answer: (a) A gas fills completely the vessel in which it is kept. Reason: The particles of a gas have very high kinetic energy and negligible forces of attraction between them. Due to this, they move randomly and at high speeds in all possible directions. As a result, they spread out and occupy all...

Question 17

Q4: Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Accepted Answer

Answer: Ice floats on water because it is less dense than liquid water. This is an exceptional property of water. Reason: When liquid water freezes to form solid ice, its molecules arrange themselves into a crystalline structure. This structure is cage-like and has a significant amount of empty spac...

Question 18

Q1: Convert the following temperature to celsius scale: a. 300 K b. 573 K

Accepted Answer

Given: Temperatures in Kelvin scale: a. 300 K b. 573 K To Find: Convert the given temperatures to the Celsius scale. Formula: The relationship between Kelvin (K) and Celsius ($^{\circ}\mathrm{C}$) scales is: Temperature in $^{\circ}\mathrm{C}$ = Temperature in K - 273 Solution: a. 300 K Temperature...

Question 19

Q2: What is the physical state of water at: a. $250^{\circ} \mathrm{C}$ b. $100^{\circ} \mathrm{C}$ ?

Accepted Answer

Answer: The boiling point of water at standard atmospheric pressure is $100^{\circ} \mathrm{C}$. a. At $250^{\circ} \mathrm{C}$: This temperature is well above the boiling point of water ($100^{\circ} \mathrm{C}$). Therefore, at $250^{\circ} \mathrm{C}$, water exists in the gaseous state (as steam o...

Question 20

Q3: For any substance, why does the temperature remain constant during the change of state?

Accepted Answer

Reason: During a change of state (such as melting or boiling), the temperature of a substance remains constant because the heat energy supplied is used to overcome the forces of attraction between the particles of the substance. This heat energy is known as latent heat (latent heat of fusion for mel...

NCERT Solutions