Matter in Our Surroundings Notes Class 9

Matter in Our Surroundings Notes Class 9

What is Matter?

The matter is anything that has mass and volume or we can say that anything that has mass, occupies space and can be felt by our one or more sense organs is called matter.

Classification of matter

(i) Since, early times, human beings have been trying to understand their surroundings. Early Indian philosophers classified matter into five basic elements, called the Panch-Tatva. These are air, water, earth, sky and fire.

(ii) Nowadays, matters are classified into groups according to their physical properties and chemical nature.
E.g. solid, liquid and gas.

Physical nature of matter

(i) Matter is made up of particles.

(ii) The particles of matter are very small or tiny.

Characteristic of particles of matter:

(1) Particles of matter are in a state of continuous movement.

(2) The particles of matter have spaces between them.

(3) Particles of matter attract each other.

States of matter

The solid-state

(i) Solids have a definite shape, distinct boundaries and fixed volumes, i.e. have negligible compressibility.

(ii) Solids have a tendency to maintain their shape when subjected to outside force.

(iii) Solids either do not diffuse or diffuse at a very low rate.

(iv) Solids may break under force, but it is difficult to change their shape, so they are rigid.

(v) Generally, solids have higher densities as compared to their liquid or gaseous forms. For examples- sugar, sand, rocks, iron, copper aluminium, etc.

The liquid state

(i) Liquids do not have a definite shape, i.e. they take up the shape of the container in which they are kept.

(ii) Liquids flow and change shape, so they are not rigid, but can be called fluid.

(iii) Solids, liquids and gases can diffuse into liquids. The gases from the atmosphere diffuse from the atmosphere diffuse and dissolve in water. These gases, especially oxygen and carbon dioxide, are essential for the survival of aquatic animals and plants. The aquatic animals can breathe underwater due to the presence of dissolved oxygen in the water.

(iv) Liquids are almost incompressible.

(v) The attraction force between the particles of liquid is greater than that of gases but less than that of solids.

(vi) 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.

(vii) Density of a liquid is generally less than that of its solid form. Some exceptions are also there, e.g. solid ice is lighter than water as it floats on water, i.e. the density of solid form of water (ice) is less as compared to that of the liquid form of water.

Water, milk, juice, oil, kerosene, petrol, alcohol, benzene etc., Are the examples of the substance which exist in the liquid state.

The gaseous state

(i) Gases also have a tendency to flow as liquids do. Therefore, they are also considered as fluids.

(ii) Gases show the property of diffusing very fast into other gases due to the high speed of particles and large spaces between them.

(iii) Gases are highly compressible. The liquefied petroleum gas (LPG) cylinder used in our homes for cooking or the oxygen supplied to hospitals in cylinders is compressed gas.

Compressed Natural Gas (CNG) is used as fuel these days in vehicles. Due to its higher compressibility, large volumes of gas can be compressed into a small cylinder and transported easily.

(iv) In a gaseous state, the particles move about randomly at high speed. Due to this random movement, gases exert pressure on the walls of the container, in which they are kept. This pressure is due to the force exerted by the particles per unit area on striking of particles with each other and to the walls of the container.

(v) All living creatures need to breathe for survival. So, solids, liquids and gases can diffuse into liquids.

Interconversion of states of matter

The phenomenon of change of matter from one state to another and back to the original state by altering the conditions of temperature and pressure is called the interconversion of states of matter.

Terms Involved in Change of State

1. Fusion or Melting and Melting point:

The process of conversion of a matter from its solid state to its liquid state at specific conditions of temperature and pressure is called fusion/melting.
And the definite temperature at which a solid starts melting is called the melting point of that solid, e.g. melting point of ice is 0°C or 273.16K.

2. Boiling and Boiling Point:

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

3. Sublimation:

The process of change of solid-state directly into the gaseous state without passing through the liquid state upon heating and vice-versa on cooling is known as sublimation.

4. Vapourisation:

The process of conversion of a matter from its liquid state to a gaseous state at specific conditions of temperature and pressure is called vapourisation.

5. Freezing and Freezing Point:

The process of conversion of matter from its liquid state to solid state at specific conditions of temperature and pressure is called freezing.

6. Condensation:

The process of conversion of matter from its gaseous state to liquid state at specific conditions of temperature and pressure is called condensation.

Latent heat of fusion

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

Effect of change of pressure

The physical state of a substance can also be changed by changing the pressure.

The pressure exerted by a gas is measured in the atmosphere (atm) unit. The pressure of air in the atmosphere is called atmospheric pressure.

Atmospheric pressure at sea level is taken as 1 atm which is also normal atmospheric pressure. As we go higher, atmospheric pressure decreases.

1 atm = 1.01× 10⁵ Pa (Pa =Pascal, SI unit of pressure)

Evaporation

The process of conversion of a liquid into its vapour state at any temperature below its boiling point is called evaporation.

Factors affecting evaporation

(i) Surface area: The rate of evaporation increases by increasing the surface area of the liquid. Evaporation is a surface phenomenon, if the surface area is increased, the rate of evaporation increases, e.g. while putting clothes for drying up, we spread them out.

(ii) Temperature: The rate of evaporation of a liquid increase with a rise in temperature. With the increase of temperature, more number of particles get enough kinetic energy to go into a vapour state. That is why evaporation is faster on a hot summer day than in winter or on a cloudy day.

(iii) Humidity: It is the amount of water vapour present in the air. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in the air is already high, the rate of evaporation decreases. That is why clothes dry up faster on a dry day than on a wet (rainy) day.

(iv) Wind speed: It is known that clothes dry faster on a windy day. This is because, with the increase in wind speed, the particles of water vapour move away from the wind, decreasing the amount of water vapour in the surroundings. That is why the rate of evaporation of a liquid increases with increasing wind speed.

Evaporation causes a cooling effect

(i) When ice-cold water is kept in a glass tumbler for some time, water droplets are observed on its outer surface.

Explanation: This occurs as the water vapours present in the air come in contact with the glass tumbler, get cooled and condensed to form these small water droplets. The formation of drops of water on the outside surface of a tumbler containing crushed ice shows the presence is water vapour in the air.

(ii) Cotton clothes are used to wear during the summer season.

Explanation: Cotton is a good absorber of water, so it helps to absorb sweat from our body. As it is obvious, the person perspires more during summer due to the auto temperature control mechanism. Hence, wearing cotton clothes helps in the easy evaporation of sweat. When this sweat evaporates, it takes the latent heat of vaporisation from our body, which in turn, cools the body. Thus, a person feels comfortable.

(iii) People sprinkle water on the roof or open ground on a hot sunny day.

Explanation: When water is sprinkled on a hot surface, it gets evaporated very quickly. As evaporated water leaves the surface cool due to the large latent heat of vaporisation of water, this technique is quite effective in summers for cooling the surface.

(iv) Liquids like acetone (nail polish remover) or alcohol placed on your palm give you a feeling of cooling.

Explanation: Acetone and alcohol are volatile liquids. When kept on the palm, their particles gain energy from the palm of surroundings and evaporate causing the palm to feel cool.

Difference between boiling and evaporation

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