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Introduction Matter Particle theory
This chunk of cheese is solid.
The orange juice is liquid.
This is exhaust gas and it's gas!

As we have found out from the introduction, anything that occupies space and has mass is matter. However, not all matter is the same. Matter, in fact, can appear as three forms: liquid, solid and gas. Water is the only kind of matter whose all three states appear in nature. Therefore, we will use water as a primary example as we go through the three states of matter. Later in the book, we will also explain the three states of matter with the particle model.

Properties of matter

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If you put water in a fridge, it freezes after a while.

The properties of matter are as follows:

  • Solids' shapes cannot be altered, and nor can its volume
  • Liquids' shapes can be altered, but not its volume
  • Gases' shapes can be altered (so it's compressible), and so can its volume

These properties can be verified with a series of experiments. First, you can try to alter the shape of volume of solids. Try doing that to your pencil – it won't budge. Then try to pour some water from a bottle to a cup. The shape changes. Now, if the bottle is full, but its size reduces, will the liquid spill? The answer is yes. Therefore, liquids have a fixed volume. Finally, try gases. If you transfer some coloured gas from one container to another, whose shapes and sizes are different, there will be no problem.

Change of states

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When you boil water in a kettle, some of it turns to gas.

Sometimes matter can change from one state to another. For example, if you blow onto the surface of glass, the water vapour that comes out of your mouth transforms into liquid. If you put the piece of glass into a freezer, a few hours later it will become ice.

There are specific names for the changes of states.







Melting, freezing and boiling happen at fixed temperatures. The temperature of distinction between different states are called the melting point, the freezing point and the boiling point. For water, these points are 0°C, 0°C and 100°C respectively. Actually, the freezing and melting points of any matter are the same.

Condensation does not take place at a fixed temperature. There is a related process called evaporation, which does not take place at a fixed temperature, although a higher temperature does accelerate the rate of evaporation. Evaporation is the process in which a solid changes into a liquid. When your wound is sterillised, it feels cold as the alcohol evaporates, carrying with it heat.

  1. X is heated, so that transforms into another state. The initial form is not liquid. What is the current form? What is the process it went through?
  2. True or false? As the boiling point of Y is 300°C, it cannot change into its gaseous form at 250°C, nor change into liquid form at 350°C.


  1. Liquid; melting
  2. False. Condensation and evaporation can happen at any temperature.