Matter in our surroundings For class 9

Matter in our surroundings

Matter: Anything that occupies space and has some mass is called matter. It exists in the form of five basic elements, the Panch tatva – air, earth, fire, sky, and water (Vayu, Prithvi, Agni, Akash, and jal).

The matter is made of particles: Everything around us is made of tiny pieces or particles. Example: A small raindrop contains about 1021 particles of water.

Evidence for particles in the matter: The random motion of small particles suspended in a gas or liquid is called Brownian motion. The existence of Brownian motion gives us two conclusions about the nature of matter:

• The matter is made up of tiny particles
•  The particles of matter are constantly moving.

Characteristics of particles of matter:

• The particles of matter have spaces between them
• The particles of matter are constantly moving
• The particles of matter attract each other.
1. The particles of matter are very, very small: When diluting the potassium permanganate solution a number of times, the color of potassium permanganate persists in the solution.
2. The particles of matter have spaces between them: When dissolving 50 grams of sugar in 100 ml of water, the volume has not increased.
3. The particles of matter are constantly moving: The best evidence that particles of matter are constantly moving comes from the studies of diffusion and Brownian motion.

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

Brownian motion: The random or zig-zag movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium, is called Brownian motion.

Ex: When we light an incense stick in one corner of a room, its fragrance spreads in the whole room quickly.

1. The particles of matter attract each other: The force of attraction between the particles of the same substance is known as cohesion. The force of attraction is maximum in solid matter and minimum in gaseous matter.

Classification of the matter: All the matter can be classified into groups:

• Solids
• Liquids
• Gases

Solids: In solids, the particles are closely packed. It is a rigid form of matter. Rigid means are unbending or inflexible.

Ex: Metal, wood, sugar, sand, rocks, and ice.

Properties of solids:

• Solids have a fixed shape and volume.
• Solids cannot be compressed much.
• Solids have high densities.
• Solids do not fill their container completely.
• Solids do not flow.
• The Force of attraction between particles is very strong.

Liquids: Constituent particles are less closely packed. Kinetic energy between the particles is more than that in solids.

Ex: water, milk, alcohol, petrol, kerosene, etc.

Properties of liquids:

• Do not have a definite shape but a definite volume.
• Density is lower than solids and can diffuse.
• Liquids generally flow easily.
• Liquids do not fill their container completely.
• Like solids, liquids cannot be compressed much.
• Liquids have moderate to high density.

Gases: Constituent particles are far apart from each other. Particles of gases have maximum kinetic energy.

Ex: Air, oxygen, carbon dioxide, hydrogen, etc.

Properties of gases:

• The Force of attraction between particles is negligible.
• Neither have definite shape nor definite volume.
• Density is least and can easily diffuse.
• Gases can be compressed easily.
• Gases fill their container completely.
• Gases flow easily.

SI and Common unit of temperature:

• SI unit of temperature is Kelvin (K).
• The common unit of temperature is degrees ‘Celsius’.
• The melting point of ice is zero degrees Celsius.
• The boiling point of water is 100 degrees Celsius.

Convert a temperature on Fahrenheit scale to Celsius scale:

C =   (F-32) x 5/9

Convert a temperature on Celsius scale to Fahrenheit scale:

F = (C x 9)/5 +32

Convert a temperature on Celsius scale to Fahrenheit scale:

K =   C + 273

Change of state of matter:

Physical states of matter can be interconverted into each other by following two ways:

1. By changing the temperature

2. By changing the pressure

Effect of change of temperature

• Solid to liquid change
• Liquid to gas change
• Gas to liquid change
• Liquid to solid change

Solid to liquid change

Melting: The process in which a solid substance changes into a liquid on heating, is known as melting. Melting is also called fusion.

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

The melting point of ice is 0 degrees Celsius.

The melting point of iron is 1535 degrees Celsius.

Liquid to gas change

Boiling: The change of a liquid substance into gas on heating is known as boiling.

Boiling point: The temperature at which a liquid boils and changes rapidly into a gas at atmospheric pressure is called its boiling point.

The boiling point of water is 100 degrees Celsius.

The boiling point of alcohol is 78 degrees Celsius.

Gas to liquid change: On cooling a gas like steam (or water vapor), the kinetic energy of its particles is lowered down, causing them to move slowly and bringing them closer, forming a liquid.

Condensation: The process of changing a gas (or vapor) to a liquid by cooling is known as condensation.

Liquid to solid change: When a liquid is cooled down by lowering its temperature, its particles lose the kinetic energy and come to a stationary position, causing the liquid to turn to solid.

Freezing: The process of changing a liquid into a solid by cooling is known as freezing. Freezing means solidification.

Freezing point: The temperature at which the state of substance changes from a liquid to a solid is called the freezing point of that substance.

Latent heat: The heat energy which has to be supplied to change the state of a substance is known as its latent heat.

Types of latent heat:

1. Latent heat of fusion: The heat energy required to convert 1 kilogram of a solid into liquid at atmospheric pressure, at its melting point is called the latent heat of fusion.
• Latent heat of fusion of ice = 3.34 x 105 J/kg.
• Ice at 0 degrees Celsius is more effective in cooling a substance than water at 0 degrees Celsius.
1. Latent heat of vaporization: The heat energy required to convert 1 kilogram of liquid into gas, at atmospheric pressure, as its boiling point, is known as the latent heat of vaporization.
• The latent heat of vaporization is 22.5 x 105 J/kg.
• Once the water has begun to boil, the temperature remains constant at 100 degrees Celsius until all the water has changed into steam.
• Water vapor at 100 degrees Celsius has more energy than water at the same temperature because particles in steam have absorbed extra energy in the form of latent heat of vaporization.

Sublimation: The changing of a solid directly into vapors on heating and of vapors into solid on cooling is called sublimation.

The common substances which undergo sublimation are Iodine, camphor, naphthalene, and ammonium chloride.

Effect of change of pressure

Gas to liquid: Gases can be liquefied by applying pressure and lowering the temperature. If high pressure is applied to a gas, it gets compressed and if the temperature is lowered, the gas is liquefied. Ammonia gas can be liquefied by applying high pressure and lowering the temperature.

Evaporation: The process of a liquid changing into vapor even below its boiling point is called evaporation.

Factors affecting the rate of evaporation

Surface area: The rate of evaporation increases by increasing the surface area of the liquid.

The humidity of air: Decrease the humidity increases the rate of evaporation.

Temperature: The rate of evaporation increases by increasing the temperature of the liquid.

Wind speed: The rate of change of a liquid increased with increasing wind speed.

Cooling caused by evaporation: Evaporation causes cooling because the process requires heat energy. The energy is taken away by the molecules when they convert from liquid to gas, and this causes cooling on the original surface.

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