Science Question Answer (2 Marks)

Why does a gas exert pressure?

When water is heated to a temperature x, it gets converted into steam at temperature x by a process called R. And when steam at temperature x is cooled, it gets reconverted in to water at the same temperature x by a process called S.

1. How much is the value of x in Kelvin?
2. What is the process R called?
3. What is the name of the energy absorbed during the process R?
4. What is process S known as?
5. What is the name of energy released during the process S known as?

Give one example of the diffusion of a solid in another solid.

Why is a liquid (the hydraulic fluid) used to operate the brakes in a car?

Give two reasons to justify that:
Water is a liquid at room temperature.

Define the term ‘latent heat of fusion’ of a solid. How much is the latent heat of fusion of ice?

Explain why, there is no rise in temperature of a substance when it undergoes a change of state though heat is supplied continuously.

Why do gases have neither a fixed shape nor a fixed volume?

Explain why, naphthalene balls kept in stored clothes in our homes disappear over a period of time.

Why does the temperature of a substance remain constant during the change of state?

State two characteristics of matter demonstrated by:
Diffusion.

When water is cooled to a temperature x, it gets converted into ice at temperature x by a process called P. And when ice at temperature x is warmed, it gets reconverted into water at the same temperature x in a process called Q.

1. What is the value of temperature x in Kelvin?
2. What is the process P known as?
3. What is the name of energy released during process P?
4. What is the process Q known as?
5. What is the name of energy absorbed during process Q?

What is the other name of homogenous mixtures?

How does applying pressure (or compression) help in the liquefaction of a gas?

State two characteristics of matter demonstrated by:
Brownian motion.

Define the term ‘latent heat of vaporization’ of liquid. What is the value of the of the latent heat of vaporization of water?

Which produces more severe burns: boiling water or steam? Why?

Whish of the following diffuses fastest and which the slowest?
Solid, Liquid, Gas
Give reasons for your answer.

Which contains more heat, 1kg of ice at 0°C or 1kg of water at 0°C? Give reason for your answer.

1. Compare the properties of solids, liquids and gases in tabular form.
2. Give two reasons for saying that wood is a solid.

During class, the students resemble molecules in a solid (because they are very close to one another)

While going from one classroom to another the students resemble molecules in a liquid (because they are a little more father apart from one another)

What does the diffusion of gases tell us about their particles?

Give two reasons to justify that:
An iron almirah is a solid.

Explain why, diffusion occurs more quickly in a gas than in al iquid.

How do solids, liquids and gases differ in shape and volume?

What is meant by ‘diffusion’? Give one example of diffusion in gases.

Give reason for the following observation:
The smell of hot sizzling food reaches us even from a considerable distance but to get the smell form cold food, we have to go close to it.

What is Brownian motion? Draw a diagram to show the movement of a particle (like a pollen grain) during Brownian motion.

A student placed a gas jar containing air in the upside down position over a gas jar full of red-brown bromine vapours. He observed that the red brown colour spread upwards into the jar containing air. Based on this observation, the student concluded that it is only the bromine vapour which moves up and diffuses into air in the upper jar, the air from the upper jar does not move down by diffusion into the lower jar containing bromine vapours. Do you agree with this conclusion of the student? Give reason for your answer.

Explain why, steam at 100°C is better for heating purposes than boiling water at 100°C.

Why does a gas fill a vessel completely?

What is sublimation? Name two substances (other than ammonium chloride) which undergo sublimation.

Draw the ‘states of matter triangle’ to show the interconversion of states of matter.

What is evaporation? State the various factors which affect evaporation.

Why does all the water of the earth not get evaporated during hot summer days?

How can the evaporation of a liquid be made faster?

An inflated balloon full of air goes down slowly (becomes smaller and smallers lowly) even though the knot at the mouth of the balloon is air tight. And after a week all the air has escaped from the balloon. Explain how the air particles got out of the balloon.

How does perspiration or sweating help keep our body cool on a hot day?

Explain the following:
When an incense stick is lighted in the corner of room, its fragrance spreads quickly in the entire room.

Honey is more viscous than water. Can you suggest why?

How is ammonia gas liquefied?

Define ‘melting point’ of a substance? What is the melting point of ice?

Name two gases of air which dissolve in water by diffusion. What is the importance of this process in nature?

Would you cool a bucket of water more quickly by placing it on ice or by placing ice in it? Give reasons for your answer.

Describe in your own words, what happens to the particles when salt dissolves in water.

Which contains more heat, 1kg of water at 100°C or 1kg of steam at 100°C? Give reason for your answer.

Why does evaporation cool a liquid?

Why are gases so easily compressible whereas it is almost impossible to compress a solid or a liquid?

Name the three states of matter. Give one example of each.

Explain briefly, how gases can be liquefied.

Why does steam cause more severe burns than boiling water?