Chapter 1 : Matter In Our Surroundings Solution
1.Convert the following temperatures to the celsius scale.
(a) 293 K (b) 470 K
Answer:
(a) 293 K – 273 = 20 °C
So, 293 K is equal to 20 °C.
(b) 470 K – 273 = 197 °C
So, 470 K is equal to 197 °C.
2.Convert the following temperatures to the kelvin scale.
(a) 25o°C (b) 373o°C
Answer :
(a) For 25°C: 25°C + 273 = 298 K
So, 25°C is equal to 298 K.
(b) For 373°C: 373°C + 273 = 646 K
So, 373°C is equal to 646 K.
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.
Answer :
(a) Naphthalene balls disappear with time without leaving any solid.
Reason: Naphthalene balls disappear due to the process of sublimation. Sublimation is a phase transition where a substance changes directly from a solid to a gas without passing through the liquid phase. Naphthalene, which is a solid at room temperature, sublimates into the air, and thus the solid naphthalene balls gradually vanish.
(b) We can get the smell of perfume sitting several metres away.
Reason: The ability to smell perfume from a distance is due to the diffusion of perfume molecules through the air. Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. The perfume molecules spread out into the surrounding air, allowing us to detect the scent from a distance
4.Arrange the following substances in increasing order of forces
of attraction between the particles— water, sugar, oxygen.
Answer: Oxygen < Water < Sugar
5.What is the physical state of water at—
(a) 25o °C (b) 0o°C (c) 100o°C ?
Answer:
The physical state of water at different temperatures is as follows:
(a) At 25°C: Water is in the liquid state.
(b) At 0°C: Water can be in both the solid (ice) and liquid states. This is the temperature at which water freezes and ice melts, so both phases can coexist.
(c) At 100°C: Water can be in both the liquid and gaseous (steam) states. This is the boiling point of water, where it transitions from liquid to gas.
6.Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
Answer:
(a) Water at Room Temperature is a Liquid
Reason 1: Type of Force Between Molecules
At room temperature (about 25°C), water is a liquid because the forces between water molecules are not too strong or too weak. Water molecules are held together by hydrogen bonds, which are strong enough to keep them close, but not so strong that they form a solid.
Reason 2: Temperature of Water
Room temperature is between the freezing point (0°C) and the boiling point (100°C) of water. At this temperature, water is in the liquid state because it is warm enough to stay as a liquid but not hot enough to turn into steam.
(b) An Iron Almirah is a Solid at Room Temperature
Reason 1: Strong Bonds Between Atoms
An iron almirah is a solid because the bonds between iron atoms are very strong. These strong metallic bonds keep the atoms in a fixed position, which makes iron hard and solid at room temperature.
Reason 2: Melting Point of Iron
Iron has a very high melting point, around 1538°C. Room temperature (25°C) is much lower than this melting point, so iron stays in the solid state.
7.Why is ice at 273 K more effective in cooling than water at the
same temperature?
Answer:
Ice at 273 K is more effective in cooling than water at the same temperature because of the latent heat of fusion.
When ice melts, it absorbs heat from the surroundings to change from a solid (ice) to a liquid (water) at the same temperature of 273 K (0°C). This heat absorption occurs without raising the temperature of the ice or the resulting water.
8.What produces more severe burns, boiling water or steam?
Answer:
Steam causes more severe burns than boiling water because of latent heat.
Latent Heat of Vaporization: Steam has extra heat energy because it absorbs heat to turn from water into gas. When steam touches your skin, it releases this extra heat, causing more severe burns.
More Heat Energy: Even though both steam and boiling water are at the same temperature (100°C), steam carries more heat energy because of the latent heat of vaporization.
9.Name A,B,C,D,E and F in the following diagram showing
change in its state
Answer: A=Melting , B= Boiling , C= Condensation , D= Freezing , E= Sublimation , F= Deposition