Matter in Our Surroundings

Question: 1. Convert the following temperatures to the Celsius scale.

(a) 293 K

Solution :

We know that,

Temp (K) – 273 = Temp in degree celsius

Thus, 293 K – 273 = `20^o\ C`

Thus, 293 K = `20^o\ C`

(b) 470 K

Solution :

We know that,

Temp (K) – 273 = Temp in degree Celsius

Thus, 470 K – 273 = `197^o\ C`

Thus, 470 K = `197^o\ C`

Question: 2. Convert the following temperatures to the Kelvin scale.

(a) `25^o\ C`

Solution:

We know that,

Temperature (K) = Temperature in Celsius + 273

Thus, `25^o\ C` + 273 = 298 K

Thus, `25^o\ C` = 298 K

(b) `373^o\ C`

Solution :

Temperature (K) = Temperature in Celsius + 273

Thus, `373^o\ C` + 273 = 646 K

Thus, `373^o\ C` = 546 K

Question: 3. Give reason for the following observations.

(a) Naphthalene balls disappear with time without leaving any solid.

Solution :

Conversion of solid into gas directly without changing into liquid and conversion from gas into solid without changing into liquid is called Sublimation.

Balls of naphthalene go under sublimation.

Thus, when balls of naphthalene left for some days it absorbs heat energy from surroundings and converted into gas because of sublimation.

This is the cause that naphthalene balls disappear with time without leaving any solid.

(b) We can get the smell of perfume sitting several meters away.

Solution :

Smell of perfume is nothing but a type of gas. Particles of gas move faster in all direction and getting mixed with air. The mixing of two gases instead of gravitation is called diffusion of gases.

Smell of perfume because of diffusion reaches to several meters.

Thus, we can get the smell of perfume sitting several meters away.

Question: 4. Arrange the following substances in increasing order of forces of attraction between the particles: water, sugar, oxygen.

Solution :

Oxygen < Water < Sugar

Explanation:

Oxygen is a gas. And force of attraction between particles of gas is lowest, i.e. negligible.

Water is a liquid. The force of attraction between particles of liquid is greater than gas but lower than solid.

Sugar is a solid. The force of attraction between particles of a solid is greatest among solid, liquid and gas.

Question: 5. What is the physical state of water at:

(a) `25^o\ C`

Solution : Water is in liquid state at `25^o\ C`.

(b) `0^o\ C`

Solution : Water freezes at `0^oC`. Thus, water is in solid state, i.e. in the form of ice at `0^o\ C`

(c) `100^o\ C`

Solution: The boiling point of water is `100^o\ C`. Thus at `100^o\ C` water is in transition phase, i.e. liquid and gaseous state. However water turns into vapour at `100^o\ C`. Thus, it can be said that water is in gaseous state at `100^o\ C`.

Question: 6. Give two reasons to justify:

(a) Water at room temperature is a liquid.

Solution :

Room temperature is generally considered between `20^o\ C` to `24^o\ C`.

A liquid has definite mass and volume but no shape.

Since, at room temperature water has definite mass and volume but water takes the shape of the container in which it is kept. Along with this, water flows at room temperature. Since, water contains all the characteristics of liquid at room temperature, thus water is liquid at room temperature.

(b) An iron almirah is a solid at room temperature.

Solution :

At room temperature, an iron almirah has definite shape, size, volume and mass, which are the characteristics of a solid. Thus, an iron almirah is a solid at room temperature.

Question: 7. Why is ice at 273 K more effective in cooling than water at the same temperature?

Solution :

Water at 273 K (`O^o\C`) has more heat energy than ice at 273 K (`O^o\C`), i.e. same temperature. Because in melting of water, heat is energy is supplied to it gets hidden as latent energy.

Thus, ice at 273 K (`O^o\C`) requires more heat energy compare to water at same temperature. Ice gets this energy from surroundings which resulting in the form of more cooling effect.

This is the cause that ice at 273 K (`O^o\C`) more effective in cooling than water at the same temperature.

Question: 8. What produces more severe burns, boiling water or steam?

Solution : Steam produces more severe burns than boiling water because

Water starts boiling at `100^o\ C` without rise in temperature even continuous supply of heat till all water turns into steam. This supplied energy is used in changing the phase from water to steam (vapour).

Thus, steam has more latent heat compare to that of boiling water.

Thus, steam produces more severe burns than boiling water.

Question: 9. Name A, B, C, D, E and F in the following diagram showing change in its state

Solution:

(A) ⇒ Heating, Melting

(B) ⇒ Heating, Vaporisation

(C) ⇒ Cooling, Condensation

(D) ⇒ Cooling, Freezing

(E) ⇒ Sublimation

(F) ⇒ Solidification, Sublimation