✔ Everything in this universe is made up of material which scientists have named “matter”.
✔ Anything which occupies space and has mass is called matter. Air and water, sugar and sand, stones, clouds, stars, plants and animals etc.
✔ Early Indian philosophers classified matter in the form of five basic elements —the “PanchTatva”—air, earth, fire, sky and water. According to them everything, living or nonliving, was made up of these basic elements.
✔ Modern day scientists have evolved two types of classification of matter based on their physical properties and chemical nature.
✔ On the basis of physical properties, matter is classified as solids, liquids and gases. ✔ On the basis of chemical properties, matter is classified as elements, compounds and mixtures.
Physical Nature of Matter
⮚ Matter is made up of particles.
⮚ Everything around us is made up of tiny pieces or particles. The particles of matter are constantlymoving (they are in motion).
⮚ The particles which make up matter are atoms and molecules.
Characteristics of Particles of Matter
⮚ The particles of matter are very, very small.
⮚ The particles of matter have space between them.
⮚ The particles of matter are constantly moving.
⮚ The particles of matter attract each other.
States of Matter
Matter around us exists in three different states– solid, liquid and gas These states of matter ariseduetothevariation in the characteristics of the particles of matter.
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Solid |
Liquid |
Gas |
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Solids have a fixed shapefixed volume. |
Liquids have fixed volume and they have no fixed shape |
Gases have neither a fixedshape but nor a fixed volume |
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Solids cannot be compressedmuch |
Liquids cannot be compressedmuch |
Gases can be compressedeasily |
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Solids have highdensities |
Liquids have moderateto high densities |
Gases have very lowdensities |
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Solids do not fill their containerCompletely. |
Liquids do not fill theircontainer completely. |
Gases fill their container completely. |
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Solids do not flow. |
Liquids generally flowEasily. |
Gases floweasily. |
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For example: Ice,coal,wood,stone,iron, etc. |
Water, milk, fruit juice, ink, petrol, etc. |
Air, oxygen, hydrogen, nitrogen, steam, etc. |
✔ The rate of diffusion of liquids is higher 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.
Brownian motion – The zigzag movement of the small particles suspended in a liquid (or gas) is called Brownian motion.
Fluid – Fluid means a material which can flow easily and requires a vessel to keep it.
Diffusion – The spreading out and mixing of a substance with another substance due to the motion of its particles is called diffusion.
✔ Diffusion is fastest in gases and slowest in solids.
✔ The rate of diffusion increases on increasing the temperature of the diffusing substance.
The liquefied petroleum gas (LPG)
Compressed natural gas (CNG)
Water can exist in three states of matter–
- solid, as ice,
- liquid, as the familiar water, and
- gas, as water vapour.
State of Matter can be changed by –
⮚ Changing the temperature
⮚ Changing the pressure
Effect of change of 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 over comes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid.
Melting point – The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
The melting point of ice is 273.16 K or 0° C.
Fusion – The change of solid state into liquid state is also known as fusion.
When a solid melts, its temperature remains the same, so where does the heat energy go?
The heat energy gets used up in changing the state by overcoming the forces of attraction between the particles and gets converted into the latent heat.
Latent heat – The heat energy which has to be supplied to change the state of a substance is called its latent heat.
Latent heat is of two types:
⮚ 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.
⮚ Latent heat of vaporisation – Latent heat of vaporisation is the heat energy required to change1kgofa liquid to gas at atmospheric pressure at its boiling point.
0 C = 273.16 K.
Kelvin is the SI unit of temperature, 0
Sublimation – A change of state directly from solid to gas without changing into liquid state (or viceversa) is called sublimation.
Effect of change of pressure
Applying pressure and reducing temperature can liquefy gases.
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.
Inter-conversion of the three states of matter
Atmosphere (atm) is a unit of measuring pressure exerted by a gas.
The unit of pressure is Pascal (Pa).
1 atmosphere = 1.01 × 105 Pa.
The pressure of air in atmosphere is called atmospheric pressure.
Evaporation
Change of state from liquid to vapour takes place without the liquid reaching the boiling point. This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.
Factors affecting Evaporation
The rate of evaporation increases with–
✔ An increase of surface area – If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out.
✔ An increase of temperature – With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state.
✔ A decrease in humidity – Humidity is the amount of water vapour present in air. If the amount of water in air is already high, the rate of evaporation decreases.
✔ An increase in wind speed – With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding.