In this chapter we discuss about Matter in our Surroundings which is important topic of class 9 science. We see a large variety of things with different shapes, sizes and textures, everything in this universe is how they are made up ? The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand – every thing is made by some units. We can also see as we look around that all the things mentioned above They all are occupy space and have mass, we try to find out the whole thing.
Matter in our Surroundings
Matter : The matter is the material of which everything in this universe, in and around us is made up of in different shapes and sizes and occupies space and has mass are considered as a Matter.
Surroundings : A definite space where covered by Matter or any substances except those space all area are considered as Surroundings.
Physical Nature of Matter
- Matter is made up of particles
- The particles of matter are very-very small.
Characteristics of Particles
- Particles of matter are continuously moving ie. they possess kinetic energy. As the temperature rises, particles moves faster because kinetic energy of the particles increases
- Particles of matter have space between them. When we make tea, coffee or lemonade (nimbu pani), particles of one type of matter get into the space between particles of the other. This shows that there is enough space between particles of matter.
- Particles of matter attract each other. When we open a water tap, try to break the stream of water with your fingers, can we do this? No, because the stream of water remains together. Particles of water are held together because of the force of attraction between them.
Kinetic Energy of Perticles : The space between the particles and kinetic energy of particles is minimum in solids, intermediate in liquids and maximum in gases.The force of attraction between the particles is strongest in solids, intermediate in liquids and weakest in gases, therefore the order of kinetic energy is given below
States of Matter
The matters are classify into three different states– solid, liquid and gas. These states of matter arise due to the variation in the characteristics of the particles of matter. Now, let us study about the properties of these three states of matter in detail
Solid State : The matter which have a definite shape, distinct boundaries and fixed volumes. This type of matter are considered as Solid Matter.
Example : Rubber band is a solid because it can change its shape under force and regains its shape when force is removed. If excessive force is applied, it breaks.
Characteristics of solid states
- Solid have definite shape and volume.
- Solid have distinct boundaries.
- Solid have rigidity and incompressibility
- The kinetic energy of Solid particles is very less
Liquid State : The matter which don`t have a definite shape, but fixed volumes. This type of matter are considered as Liquid Matter.
Characteristics of liquid state
- Liquid have fluidity i.e., they are not rigit.
- They are low compressibility.
- They don`t have definite shape and boundaries ie: they take the shape of the vessels.
- Solid Have definite volume.
They take the shape of the container in which they are stored. The gases (oxygen and carbon dioxide) from the atmosphere diffuse and dissolve in water. Due to these gases aquatic Plants and Animal are able to survive. Diffusion is much more in liquids than in solids due to free movement of particles of liquids.
Gaseous State: The matter which don`t have a definite shape, and don’t have a fixed volumes. This type of matter are considered as Gaseous Matter.
Characteristics of gaseous state are
- They have Have fluidity.
- They have high compressibility.
- They have no definite boundaries.
- They haven’t definite shape.
- They have no definite volume
The particles in a gas are free to move in any direction hence gases can flow Gases are substances that do not have fixed volume and occupy all the volume available to them. Pressure of gas is the force applied on the walls of vessel by the irregular moving gas particles.
Change of State of Matter
Mater can exist in three states of matter i.e. solid – ice, liquid – water, gas – water vapour.
Solid + heat →liquid
Liquid + heat → Gas
On heating ice melts into water and then converts into water vapours. Change in the physical state of matter can be done in two ways:
1. By Changing the 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 the solid melts and is converted to a liquid.
Melting Point: The temperature at which a solid melts to form liquid at atmospheric pressure is called its melting point. Melting point of ice is 273.16 K (0″ C). During melting the temperature ofice does not rise even though heat is being supplied continuously due to latent heat of fusion. This latent heat of fusion is used up to overcome the forces of attraction between ice particles. At 0″ C energy of water particles is much more than the energy of particles of ice at 0° C.
Latent Heat of Fusion
The amount of heat required to change 1 kg solid to its liquid state (at its melting point) at atmospheric pressure.
Boiling Point: The temperature at which a liquid boils to form vapours at atmospheric pressure is called its boiling point. Boiling point of water is 373 K (100 C+ 273-373 K)
Latent Heat of Vapourization
The amount of heat required to change 1 kg liquid to its gaseous state (at its boiling point) at atmospheric pressure. During boiling the temperature of water does not rise even though heat is being supplied continuously as this heat of vaporization is used up to over the forces of attraction between water particles.
At 100° C, energy of water vapours is much more than the energy of water at 100° C. So, we can change one Reaction At 25°C, water is liquid. At 0″ C, water is solid (ice). At 100° C, water is gaseous state (steam).
Sublimation: The change of solid directly into vapours on heating and of vapours into solid on cooling without passing through the intervening liquid state is called sublimation
Example: When camphor or ammonium chloride is heated in a China dish covered by a inverted funnel (with cotton plug in its upper open end), the vapours of ammonium chloride are converted into solid ammonium chloride on coming in contact with the cold inner walls of the funnel.
2. Effect of Change of Pressure
If we compress a gas in a cylinder, the distance between the particles of gas is reduced and finally gas is liquefied on lowering temperature. By applying high pressure, the particles of a gas can be brought close together. Solid carbon dioxide (dry ice) is changed into carbon dioxide gas
directly without changing into liquid when pressure is reduced to one atmospheric pressure. Thus, states of matter te.. solid. quid, gas are determined by temperature & pressure.
Evaporation: A surface phenomenon in which liquid changes into vapours at any temperature below its boiling point is called evaporation. Particles on the surface of a liquid have higher kinetic energy than others, so they break. The forces of attraction between the particles & escape from the surface of liquid in the form of vapours.
Factors affecting evaporation
Rate of evaporation depends on following factors as given below.
- Exposed surface area: On increasing surface area of liquid, rate of evaporation increases.
- Increase in temperature: Increases kinetic energy of particles hence rate of evaporation increases.
- Humidity: When the humidity of air (degree of dampness of air) is low, evaporation rate is increased. More humidity, less evaporation.
- Wind: When wind speed increases, rate of evaporation also increases
Evaporation always causes cooling The cooling caused by evaporation is based on the fact that when a liquid evaporates, it takes latent heat of vaporization from surroundings which on losing heat get cooled. Examples
When we put acetone on our hand, it gets evaporated by taking heat from our hand and our hand feels cool. We should wear cotton clothes in summer to keep cool and comfortable as cotton is good absorber of water, so it absorbs the sweat from our body and exposes it to air for evaporation of sweat thus cools our body. Often people sprinkle water on ground during summer. This water takes heat from ground and surrounding air to evaporate, thus making the place cool