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Diffusion: Intermixing of particles of two different types of matter on their own is called diffusion.

Why diffusion takes place? 

Diffusion is proccess in which particles of matter get intermixed on their own, this happens due to enterance of particles into the spaces.

Solids, liquids and gases these states of matter arise due to the variation in the characteristics of the particles of matter.

Diffusion in Liquids: Solids gases and liquids can diffuse into liquids. The rate of diffusion is higher in liquids than that of solids. This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state.

Diffusion of gases in liquids : The aquatic animals can breathe under water due to the presence of dissolved oxygen in water.

Diffusion In Gases : gases are highly compressible as compared to solids and
liquids. In gasious states particles have very less attraction force and larger space between them as compared to other states. Due to this faster movement and having larger space the process of diffusion take place very fast. 

Gases exerted pressure on the wall of containner: In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.

The Changing in states of matter: 

There are following reasons to change in states of matter:

1. Increasing and decreasing in space between particles can be changed in states. 
2. If increasing and decreasing in movement of particles can be changed in states. 
3. if the attraction force between particles is increased or decreased then states of matter can be changed. 

Above all points indicate that the changing in states is due to change in differents charactristics of matter. 

These are following physical quantities that can change the states of matters. 

Physical factors which changes the states: 

(i) Temperature

(ii) Pressure

TEMPERATURE 

1. Temperature: On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when converted to a liquid.

So the state of matter can be changed into another state by changing
the temperature.

The S.I unit of Temperature is Kelvin (K). 

But there are also other units which are used to measure the temperature. These are Celsius (^०C) and Fahrenheit (^०F). 

We can also convert the Kelvin into Celsius and Celsius into Kelvin. And also can convert Celcius to Fahrenheit and so on. 

0^० C = 273 K    

To change a temperature on the Kelvin scale to the Celsius scale you have to subtract 273 from the given temperature, and to convert a temperature on the
Celsius scale to the Kelvin scale you have to add 273 to the given temperature.

For Example converting Celsius to Kelvin We have to add 273 into Celcius Value: 

15^० C = 15 + 273 K = 288 K 

Similarily converting Kelvin into Celsius We have to substract 273 from given Kelvin value. 

293K = 293 - 273 ^० C = 20^० C 

The physical states of water on various temperature:

States	Temperature	Name of matter
solid	0 oC	Ice
Liquid	25 oC	Water
Gas	100 oC	Water-vapour

Melting Point: The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.

Note:- The different materials have different melting point.

Example: The melting point of Ice is 0 ^०C.

Boiling Point: The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

Note:- The different materials have different boiling point.

Example: The boiling point of Ice is 100 ^०C.

SI unit of temperature is Kelven(K).

Changing temperature Scale:

Kelvin to celsius scale:

Converting kelving scale into kelvin, It is 273 is substracted from kelvin value to get celsius temperature.

And 273 is added to get kelvin temperature.  

Example: 

(i) Convert 320 K into celsius scale

Solution: 

320 K = 320 - 273 ^०C

          = 47 ^०C

Celsius to Calvin. 

(ii) Convert 25 ^०C into kelvin scale

Solution:

25 ^०C = 25 + 273 K

          = 298 K

Latent heat: 

​During process of melting, the temperature of the system does not change after the melting point is reached, till the any solid does not melt completely. This heat gets used up in changing the state by overcoming the forces of attraction between the particles. As this heat energy is absorbed by solid without showing any rise in temperature. This hidden temperature is known as latent heat. 

Latent heat of fusion: 

The amount of heat energy that is required to change 1 kg of a solid into
liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. 

So, particles in water at 00 C (273 K) have more energy as compared to particles in ice at the same temperature.

Latent heat of vaporisation: 

Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

PRESSURE:

2. Pressure : We know that increasing or decreasing space between particles of matter can change its state. if we have to change states of matter, pressure does the same work. Similarily increasing or decreasing pressure causes change in states.  Example: Very large quantity of gases is filled in a small cylinder by compression (pressure) to change it in liquid form.

 

Temperature and pressure is responsible to change the states of matter. 

Dry Ice: 

Solid CO₂ is stored under high pressure.  Solid CO₂ gets converted directly to gaseous state on decrease of pressure to 1 atmosphere* without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

• Solid carbon dioxide is known as dry ice. 

Exerting pressure on CO₂ gas It convert into Solid CO₂ .