Chemical Change and Physical Change
There are two kinds of change－chemical change and physical change.
In a chemical change, there is always a new substance formed.Breaking up water into hydrogen and oxygen is a chemical change.In each of the chemical change at least one new substance is formed.A change is not a chemical change if it doesn't form a new substance.
Physical changes are very common, too.There are many examples.You can make a physical change by tearing a piece of paper into two, or by cutting a piece of iron with a lathe.Here the paper is still paper, and the iron is still iron.
Another way of making physical change is dissolving something in water.When you dissolve salt in water, the salt disappears.You may think that a new substance has been formed.But in fact there is no new substance.The salt is still salt.You can still taste it.So the dissolving of anything is a physical change.
When water freezes, the change is also a physical one.The water changes from liquid to solid.But it is still the same substance.That is why the freezing of anything is a physical change.
And people often tell the differences between a chemical change and a physical change through some experiments.We should try to explore the magical science world by doing experiments by ourselves.
[阅读障碍词]
1．hydrogen n．氢气
2．tear v．撕扯
3．lathe n．车床
4．freeze v．结冰；冷冻
5．magical adj.魔力的
