Class 9 Science Chapter 1 Matter in Our Surroundings
- Expand:
a) CNG: Compressed Natural Gas
b) LPG: Liquefied Petroleum Gas - Define latent heat.
Latent heat is the amount of heat required to change the state of a substance without changing its temperature. - Define melting point of a substance.
The melting point is the temperature at which a solid changes into a liquid at atmospheric pressure. - Define boiling point of a substance.
The boiling point is the temperature at which a liquid changes into a gas at atmospheric pressure. - Give the relation between Celsius scale and Kelvin scale of temperature.
( K = ^\circ C + 273 ) - Evaporation is called a surface phenomenon. Comment.
Evaporation occurs only at the surface of a liquid, where particles gain enough energy to escape into the gas phase. - Which substance in its gaseous state is called vapour?
A substance in its gaseous state, below its boiling point, is called vapour. - Give reason: “Water droplets form on the outer surface of a glass containing ice-cold water.”
The air surrounding the glass cools down, leading to the condensation of water vapour into liquid droplets on the glass surface. - Convert:
a) 280 K = 280 – 273 = 7°C
b) -23°C = -23 + 273 = 250 K - Though sponge is a solid, we are able to compress it. Why?
Sponge contains tiny pores filled with air, which allows it to be compressed when the air is expelled from the pores.