There are many factors that can bring about changes in various substances. These changes are of two types:
(i) Reversible change
Changes that can be reversed are Reversible changes. This means the object or substance that undergoes the change can be restored to its original state.
Examples of reversible change
- When air is blown into a balloon, it fills up completely and when the air is released, the balloon deflates to its original shape and
- Paper folded to make plane models can be unfolded to get its original
(ii) Irreversible change
Irreversible changes are the changes that cannot be reversed. This means the object or substance that undergoes the change, cannot get back to its original state.
Examples of irreversible change
- When a balloon filled with air is pricked, it bursts. The pieces of the balloon cannot be joined to get the complete structure as the one
- A piece of paper cut in the shape of an aeroplane cannot be stuck back together to get the original
What are some of the factors that cause changes?
In the above examples, the changes were caused by physical actions like blowing, folding, bursting and cutting. But there are other factors that can also cause changes. Some of them are:
● Change in temperature
Changing the temperature of a substance can bring about changes.
For example, reducing the temperature of water can freeze it to ice or heating the ice can change it to water.
But changing the temperature will not always reverse the change.
For example, increasing the heat while cooking can burn vegetables. But taking the vegetables off the fire and cooling them, will not bring them back to a properly cooked state.
● Addition of a substance
Adding a substance can also bring about changes.
For example, adding a little amount of curd to warm milk changes the milk to curd.