Change of state of matter

Why Solids, Liquids and Gases Have Different Properties

According to the kinetic theory of matter, the particles of matter are in continuous motion.

Some force of attraction tends to hold the particles together and control their movements.

To Show that Liquids do not have a Fixed Shape but they have a Fixed Volume

Does Gases have fixed shape and fixed volume why?

Why Solids and Liquids Cannot be Compressed but Gasses Can be Compressed Easily?

 

Diffusion

Diffusion is a property of matter which is based on the motion of its particles. Diffusion is fastest in gases and slowest in solids. The rate of diffusion increases on increasing the temperature.

Illustration

When someone opens a bottle of perfume in one corner of a room, its smell spreads in the whole room quickly. Why?

Solution

This happens because the particles of perfume (GAS) move rapidly in all the directions and mix with the moving particles of air in the room.

Illustration

Give reasons for the following observation. The smell of hot sizzling food reaches you several meters away, but to get the smell of cold food you have to go close.

Solution

The vapours of hot food diffuse in air readily but the cold food does not evaporate so fast so its particles cannot diffuse quickly in air and its smell cannot travel long distance.

The Common Unit of Temperature and SI Unit of Temperature

We use Celsius scale of temperature for measuring temperatures in our everyday life.

The laboratory thermometers which we use for performing science experiments the clinical thermometer which we use for measuring human body temperature

K = oC + 273
OoC = 273K

Illustration

Convert the following temperature to Celsius scale

  • 300K
  • 573K

Solution

For converting Kelvin to Celsius, the formula is

K – 273 = oC

  • 300K – 273 = 27oC
  • 573K – 273 = 300oC

Illustration

Convert the following temperature to Celsius scale

  • 293K
  • 470K

Solution

For converting Kelvin to Celsius, the formula is

K – 273 = oC

  • 293K – 273 = 20oC
  • 470K – 273 = 197oC

Illustration

Convert the following temperature to Kelvin scale

  • 25oC
  • 373oC

Solution

For converting Celsius to Kelvin, the formula is

oC + 273 = K

  • 25oC + 273 = 298K
  • 373oC + 273 = 646K

Change of state of matter

We can change the physical state of matter in two ways:

  • By changing the temperature, and
  • By changing the pressure.

Solid to Liquid Change: Melting

The process, in which a solid substance changes into a liquid on heating, is called melting (or fusion).

Illustration

For any substance, why does the temperature remain constant during the change of state?

 Solution

During the change of state, the temperature becomes constant, because the heat provided is utilized for breaking the attraction force between the particles of the substance. This happens at melting point (or boiling point) of the substance and the heat used is called the latent heat of fusion (or vaporization). During condensation or solidification, the vice-versa happens.

Liquid to Gas Change: Boiling (or Vaporization)

Place during boiling. The boiling of a liquid takes place at a fixed temperature. The temperature, at which a liquid boils and changes rapidly into a gas at atmospheric pressure, is called boiling point of the liquid.

When a liquid is heating, it changes its physical state and becomes a gas.

Illustration

What would be the temperature when water starts boiling?

Solution

As the water starts boiling, the temperature will be 100oC or 373 K.

Illustration

What is the temperature when all the water has boiled?

Solution

The temperature remains constant i.e., 100oC during its complete boiling process.

Illustration

Under which condition, we can boil water at room temperature?

Solution

We can boil water at room temperature 1 atomic pressure.

Illustration

At what temperature boiling takes place?

Solution

Boiling takes place only at boiling point.

Gas to Liquids Change:- Condensation

The process of changing a gas to liquid by cooling is called condensation.

Liquid to Solid Change: Freezing 

The process of changing a liquid into a solid by cooling is called freezing.

When a liquid is cooled its particles lose energy due to which they move slowly.  At this stage the liquid freezes and becomes a solid.

Illustration

Give reason for the observations.  We can get the smell of perfume sitting several meters away?

Solution

The smell o aroma of perfume reaches several meters away due to the fast diffusion of the gaseous particles of perfume through air.