States of matter solid liquid and Gases

States of matter solid liquid and Gases

All things, whether living or non-living, are made of matter. Anything that has mass and occupies space is called matter. Table, chair, water, milk, air, etc., are matter. matter is made up of very small particles called molecules. on the bases of arrangement of molecules, matter exists in three states-- solid, liquid and gas.

ARRANGEMENT OF MOLECULES

Solids: In solids, molecule;es are very closely packed. there is a strong force of attraction between them. They cannot move away from one another. So, solids are hard, rigid, have fixed shape and volume, and cannot flow.

Liquids: In liquids, the molecules are not very close to one another due to weak force of attraction between them. So, the molecules in liquids can move and slide over each other. This makes liquids flow. Liquids take the shape of the container in which they are poured into. So, liquids do not have a fixed shape but have a fixed volume.

Gases: In gases, the force of attraction between the molecules is the weakest. So the molecules in gases  are far apart from one another and they are free to move. This makes the gases flow easily and fill the container completely in which they are kept. So, gases neither have a fixed shape nor a fixed volume.

CHANGE OF STATE

In previous classes, you have learnt that the state of matter can be changed from one form to another on heating or cooling. Do you know how this happens? Do you know how this happens? Let's see the effect of heating or cooling on the molecules of matter.

EVAPORATION

The change of a liquid into gaseous state on heating is called evaporation. When water is heated, it changes into water vapour. This is because, on heating, water molecules start moving faster. they become free and escape into the air in the form of water vapor and can move much more freely.

Condensation 

When steam gets cooled, it condenses to form water again. This happens because on cooling steam, the movement of water molecules becomes slower. They start moving close to one another. They become less free to move and thus come closer to one another to form water. The change of a gas into liquid state on cooling is called condensation.

Melting 

Ice is solid. When it is kept at a warm place, the movement of molecules of ice increases. They become free from the rigid form and thus become loosely packed and form water. The change of a solid into liquid state on heating is called melting.

Freezing

When you cool water, the movement of its molecules slows down. They come very close to one another and pack into a rigid shape to form ice. The change of a liquid into solid state on cooling is called freezing.

SOLIDS IN WATER

Take a glass of water. Add a few crystals of sugar in it and stir. You find that the particles of sugar disappear. Where have the sugar particles gone? The particles of sugar take up the space between the molecules of water. So, we say that sugar gets dissolved in water.

LIQUIDS IN WATER

You must have seen a painter removing paint from his hand by using turpentine oil, not with water. This is because paint gets dissolved in turpentine oil and is easily removed, whereas it does not dissolve in water.

Some liquids when mixed together dissolve in each other. They are called miscible liquids. For example, liquids like glycerine and milk dissolve in water. Some liquids when mixed together do not dissolve in each other. They are called immiscible liquids. For example, kerosene iol and vegetable oil do not dissolve in water.

GASES IN WATER

When you boil water, you observe some bubbles are formed along the sides of the vessel. These are the dissolved gases that get separated from water on heating. Gases like carbon dioxide, oxygen and nitrogen dissolve in water. For example, water in rivers, oceans and lakes has oxygen dissolved in it. When we open a bottle of aerated drink, bubbles of carbon dioxide gas come out. Carbon dioxide gas is dissolved in water under great pressure.

EXPANSION AND CONTRACTION OF MATTER

When we heat a substance, its size increases. This increase in size of matter is called expansion of matter. On heating, s substance expands or its size increases because the movement of molecules increases and the space between them also increase.

For example, to open a tight metal lid of a jar, we dip it into hot water because the heat of water expands the lid a little and it opens out easily.

When we cool a substance, its size decreases. This decrease in size of matter is called contraction of matter. On cooling, a substance contracts or its size decreases because space between them decreases. That is why, electric cables do not appear loose in winter, while they hand loosely from poles in summer.

PHYSICAL AND CHEMICAL CHANGES

1. Physical Change

When the change occurs only in the shape, size and state of matter, it is called a physical change. It is a temporary change and can be reversed. No new substance is formed during this change.

Physical change may occur due to heating and cooling. For example, when you heat water, it changes into steam. On cooling steam, it changes again into water. Similarly, when you freeze water, it changes into ice. Stretching of a rubber band is also a physical change.

 

2  Chemical Change

When matter changes altogether to form a new substance, it is called a chemical change. It is a permanent change and cannot be reversed. For example, burning of paper. When we burn paper, it changes into a completely new substance called ash and we cannot get back the paper.