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2. Classification of matter:

- Study of matter is simplifed by its classification.

-Matter is classified according to its state and physical properties.

-States of matter - Matter is classified based on state as follows - solids, liquids and gases

-Same substance (matter) can exist in three different states at different temperatures. Let us take water as an example. In solid state we see it as ice. In liquid state we see it as water. In gaseous state we call it water vapour.

-Solid has definite shape, mass and volume. Example - book, brick etc. The volume of a solid can be changed only by applying external force.

-This is because the molecules in a solid are closely packed as if in fixed positions. There is not much space between particles inside a solid. So it is not easy to change the shape of a solid. I.e. a solid cannot be easily compressed or expanded.

-Liquid has mass and volume but no definite shape. It flows to take the shape of its container. It cannot be compressed to a smaller volume.

-Since liquid can flow, it can be poured from one container to another. But a given volume of a liquid remains unchanged by pouring or transferring it from one container to another. This implies, a given amount of liquid has fixed volume.

-Real life example - take 100ml water with a measuring cylinder and pour it in a 1000ml (1 litre) bottle or jar. The volume of water inside the bottle or jar still remains 100ml.

-This is because, molecules in a liquid are not in fixed positions and there is space between these molecules. This allows them to move to some extent and take the shape of the container when we pour or transfer. But at the same time they are not so far apart that they can expand to take the shape of the container.

-Gases have no definite shape or volume. They expand to occupy the space or volume available. So the volume of gas in a container, say a cylinder, is equal to the volume of the cylinder.

-They can also be compressed to a limited space or volume. In other words they can be easily expanded or compressed to fill a container.

-Real life examples - when we blow a balloon the air or gas we pump in, fills up the space in the balloon. Thus the air or gas also takes the shapw of the balloon. Another E.g. is that a cycle or car tyre has air in it. But we can pump more air into it by compressing the air inside.

-This is because molecules of a gas are loosely packed. There is lot of space between them. (About 1000 times more space than those in liquids). This allows them to move more freely than the particles of liquid.

-Oxygen, hydrogen, carbon dioxide, nitrogen are all examples of gases. Air is a mixture of gases. It has 78% nitrogen and 21% oxygen

http://jonkey.blogspot.com/2006/09/chemistry-unit-1-matter-and-its.html

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