Question:
What is evaporation? Why does evaporation cause cooling?
Answer:
The process in which a liquid change into its vapour state at temperatures below the boiling point is called evaporation. Evaporation is an endothermic process i.e. liquid absorbs heat during evaporation. This heat may be provided either by the surroundings or by liquid itself. When the evaporating liquid takes the required heat from other parts of the liquid, the rest of the liquid cools down. On the other hand, if the liquid takes heat from the surroundings, it causes cooling of the surroundings. E.g. on a hot day (sunny day), we perspire. When this sweat evaporates, it absorbs the required heat from our body, and we feel cool.
Matter in Our Surroundings
Q 1.
What is SI unit of temperature? Give mathematical relation also.
Q 3.
How matter is classified in terms of physical state?
Q 4.
What do you mean by change in state?
Q 5.
List any five physical properties of liquids.
Q 6.
What is evaporation? Why does evaporation cause cooling?
Q 7.
What do you mean by the term Volume?
Q 8.
What are the ways a gas can be liquefied?
Q 9.
Why solids cannot be compressed like gases?
Q 10.
Define the term Volatile Liquid.
Q 11.
Which state of matter is most easily compressible?
Q 12.
Define transpiration.
Q 13.
Arrange the following substances in increasing order of intermolecular force of attraction: water, sugar, oxygen
Q 15.
What are the differences between boiling and evaporation?
Q 16.
Define evaporation.
Q 17.
What do you mean by the following terms:
a. Evaporation
b. Sublimation
c. Condensation
Q 18.
Our own bodies contain examples of all three states of matter. Can you identify these?
Q 19.
Why is light not considered matter?
Q 20.
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.
Q 21.
Define Latent Heat of Fusion and Latent Heat of vaporisation.
Q 22.
How can matter change its state?
Q 23.
How matter is classified in terms of composition?
Q 24.
Why do gases diffuse rapidly?
Q 25.
Why do diffusion become faster at higher temperatures?
Q 26.
What is the physical state of water at the following temperatures? (a) 25 °C (b) 0 °C (c) 100 °C
Q 27.
Which of the following state does not exist at room temperature conditions: a) Solids b) Liquids c) Gas d) Plasma
Q 28.
How vapour is different from gases? Give examples of each.
Q 29.
In which case evaporation of water will be faster i.e. near the sea or far away from the sea.
Q 30.
Convert the temperature of 373°C to the Kelvin scale.
Q 31.
Name the process by which a drop of ink spreads in a beaker of water.
Q 32.
What is the (a) common unit of temperature, and (b) SI unit of temperature ?
Q 33.
What causes evaporation?
OR
Explain evaporation and its cooling effect in terms of kinetic energy of particles.
Q 34.
Give the usual name for the following :Heat required to change the state of a substance without changing the temperature.
Q 35.
Which of the following are matter?
Chair, Air, Love, Smell, Hate, Almonds, Thought, Cold, Cold drinks, Smell of perfume
Q 36.
Why do solids expand a bit on heating and contract a bit on cooling?
Q 37.
What is the general name of : (a) rigid form of matter ? (b) fluid forms of matter ?
Q 38.
Write the full forms of the following :(a) LPG (b) CNG
Q 39.
The Kelvin temperature is 270 K. What is the corresponding Celsius scale temperature ?
Q 40.
Why does the temperature of a substance remain constant during melting and boiling even when heat is being supplied to it continuously?
Q 41.
Is smell of garlic or perfume a matter?
Q 42.
Convert the temperature of 573 K to the Celsius scale.
Q 43.
The Kelvin scale temperature is 0 K. What is the corresponding Celsius scale temperature ?
Q 44.
Write the relation between Kelvin scale and Celsius scale of temperature.
Q 45.
(a) What is evaporation ? State the various factors which affect evaporation.
Why does evaporation cool a liquid ?
Q 46.
Give reasons for the following observations. The smell of hot sizzling food reaches you several meters away, but to get smell from cold food you have to go close.
Q 47.
Convert the following temperature to Celsius scale: (a) 300 K (b) 573 K
Q 48.
Give reasons to justify: (a) Water at room temperature is a liquid. (b) An iron almirah is solid.
Q 49.
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.
Q 50.
What are the conditions for 'something' to be called 'matter' ?
