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.
What do you mean by change in state?
Q 4.
How matter is classified in terms of physical state?
Q 5.
What is evaporation? Why does evaporation cause cooling?
Q 6.
What do you mean by the term Volume?
Q 7.
Define the term Volatile Liquid.
Q 8.
Which state of matter is most easily compressible?
Q 9.
List any five physical properties of liquids.
Q 10.
What are the ways a gas can be liquefied?
Q 11.
Arrange the following substances in increasing order of intermolecular force of attraction: water, sugar, oxygen
Q 12.
Define transpiration.
Q 13.
Why solids cannot be compressed like gases?
Q 15.
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 16.
How matter is classified in terms of composition?
Q 17.
Define evaporation.
Q 18.
Our own bodies contain examples of all three states of matter. Can you identify these?
Q 19.
What are the differences between boiling and evaporation?
Q 20.
What do you mean by the following terms:
a. Evaporation
b. Sublimation
c. Condensation
Q 21.
Define Latent Heat of Fusion and Latent Heat of vaporisation.
Q 22.
Why is light not considered matter?
Q 23.
Why do diffusion become faster at higher temperatures?
Q 24.
How can matter change its state?
Q 25.
How vapour is different from gases? Give examples of each.
Q 26.
In which case evaporation of water will be faster i.e. near the sea or far away from the sea.
Q 27.
Which of the following are matter?
Chair, Air, Love, Smell, Hate, Almonds, Thought, Cold, Cold drinks, Smell of perfume
Q 28.
What is the physical state of water at the following temperatures? (a) 25 °C (b) 0 °C (c) 100 °C
Q 29.
Which of the following state does not exist at room temperature conditions: a) Solids b) Liquids c) Gas d) Plasma
Q 30.
Convert the following temperature to Celsius scale: (a) 300 K (b) 573 K
Q 31.
Why does the temperature of a substance remain constant during melting and boiling even when heat is being supplied to it continuously?
Q 32.
Explain compressibility in gases with an example?
Q 33.
Why do gases diffuse rapidly?
Q 34.
Define the following terms:
a. Melting point
b. Freezing point
c. Boiling point
Q 35.
What factors affect the rate of evaporation?
Q 36.
The Kelvin scale temperature is 0 K. What is the corresponding Celsius scale temperature ?
Q 37.
Why is ice at 273 K more effective in cooling than water at the same temperature?
Q 38.
Name the process by which a drop of ink spreads in a beaker of water.
Q 39.
State whether the following statement is true or false : Solid carbon dioxide is stored under low pressure.
Q 40.
What is meant by saying that the latent heat of vaporisation of water is 22.5 x
Q 41.
Explain with an experiment to show gases do not have fixed shape or volume.
Q 42.
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 43.
What is the (a) common unit of temperature, and (b) SI unit of temperature ?
Q 44.
Is smell of garlic or perfume a matter?
Q 45.
The Kelvin temperature is 270 K. What is the corresponding Celsius scale temperature ?
Q 46.
Give the usual name for the following :Heat required to change the state of a substance without changing the temperature.
Q 47.
(a) What is evaporation ? State the various factors which affect evaporation.
Why does evaporation cool a liquid ?
Q 48.
What are the characteristics of matter?
Q 49.
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 50.
Give reasons to justify: (a) Water at room temperature is a liquid. (b) An iron almirah is solid.
