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What are physical changes?
Physical changes are changes in the condition of a substance, but not changes in its chemical properties.
Physical properties
Different substances have different physical properties, such as how they look, and their melting and boiling points. For example, nitrogen, water and iron are three substances with very different properties. The table shows some of their properties.
| Property |
Nitrogen |
Mercury |
Iron |
| Colour |
colourless |
silvery |
grey |
| State at room temperature |
gas |
liquid |
solid |
| Melting point (°C) |
–210 |
–39 |
1538 |
| Boiling point (°C) |
–196 |
357 |
2861 |
| Density (g/cm3) |
0.0012 |
13.6 |
7.9 |
| Is it magnetic? |
no |
no |
yes |
| Does it conduct heat well? |
no |
yes |
yes |
| Does it conduct electricity well? |
no |
yes |
yes |
| |
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You can see from the table that it would be easy to tell these substances apart. Nitrogen is the main gas in the air, mercury is the only liquid metal, and iron is the only one of the three that is magnetic.
Physical changes
Physical changes in a substance are changes such as melting, boiling and change in colour. The substance does not change its chemical properties. For example, iron will still react with oxygen to form iron oxide, even when it is a hot liquid.
The mass of the substance stays the same during a physical change. For example, if you freeze 100g of water, you get 100g of ice. And if you boil 100g of water, you get 100g of steam.
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