Chapter - 1
Matter in Our Surroundings
️ Substance :-
The material of which everything in the universe is made of is called matter and everything around us has matter.
Matter occupies space and has mass.
️ Physical properties of particles :-
- Matter is made up of particles.
- It is not continuous.
- The particles of matter are very small.
Characteristic properties of particles of matter :-
- Particles of matter are in constant motion. That is, they have kinetic energy.
- There is a space between the particles of matter.
- Particles of matter attract each other.
️ States of matter :-
Physically matter is found in three states :-
- (i) solid state
- ( ii ) Liquid phase
- (iii) gaseous state
We can also divide the human body into three states of matter .
- (i) Bones and Teeth – Solid State
- (ii) (Blood) Blood and water – liquid state
- (iii) Air in the lungs – gaseous state
️ Solid State :-
- has a certain size.
- There are clear boundaries in the solid state.
- Has a fixed or fixed volume.
- Their compressibility is negligible.
- They are strong.
❇️ Liquid state :-
- Liquids are liquids, they have a flow.
- A liquid has no fixed shape. They take the shape of a pot.
- A liquid has a fixed volume.
- Liquids have very little compression.
️ Gaseous state :-
- Gases flow.
- Compression is high in gases.
- Gases have no definite boundaries.
- Gases do not have a definite shape.
- Gases do not have a fixed volume.
️ Change in the states of matter :-
Water is found in all three states of matter.
- solid ice
- water - liquid
- gaseous - vapor
On heating, ice turns into water and water turns into vapour. The physical state of matter can be changed in two ways.
- (a) change in temperature
- (b) effect of pressure change
️ Change in temperature :-
Melting point :-
The temperature at which a solid melts into a liquid at atmospheric pressure is called its melting point.
The melting point of ice is 273.16 K. For convenience, we take it as 0°C i.e. 273 K.
Latent heat of fusion :-
1 kgf at atmospheric pressure. The amount of heat energy required to convert a solid into a liquid at its melting point is called latent heat of fusion.
So the particles of water at 0°C have more energy than the particles of ice at 0°C.
Boiling Point :-
The temperature at which a liquid starts boiling at atmospheric pressure is called its boiling point.
Boiling point is a population property. Boiling point of water = 373 K ( 100°C + 273 = 373K ) =
When water is boiled, its temperature does not increase, the temperature remains 100°C because the latent heat of vaporization breaks the force of attraction between the water particles.
So the particles of vapor at 100°C have more energy than the particles of water at the same temperature.
A change in temperature can change the state of matter from one to another, as shown in the diagram below.
🔶 Uplift :-
There are some substances which change directly from solid state to gas and back to solid without changing into liquid state. This process is called sublimation.
️ (b) Effect of change of pressure :-
If we take a gas in the cylinder on decreasing the temperature and compress it, then the distance between the particles will decrease and the gas will turn into a liquid.
Increasing pressure + decreasing temperature → converting gas to liquid
- By increasing the pressure, the particles of the gas come closer.
- Solid Carbondioxide (solid carbon dioxide) [dry ice] can be converted back to gaseous CO2 (carbon dioxide) without changing to the liquid state. For this, the pressure has to be reduced to 1 atmosphere.
dry ice - solid carbon dioxide
️ Evaporation :-
A surface process in which surface particles in liquid substances change into vapor at any temperature below the boiling point. Such a process is called evaporation.
️ Factors affecting evaporation :-
Surface Area: Increasing the surface area increases the rate of evaporation.
Increase in temperature: The rate of evaporation increases with increasing temperature because the kinetic energy of the particles of matter increases.
Humidity: If there is humidity in the air then the rate of evaporation decreases.
Wind speed: If the wind speed increases, the rate of evaporation also increases.
️ Cooling by evaporation :-
During the evaporation process, the particles of the liquid absorb the energy from their surroundings to recover the lost energy. Due to this absorption the atmosphere becomes cooler.
