1-Are all changes desirable ? which can be undesirable changes
2-Explain how is burning paper diffrent from tearing paper
Dear Student,
The answers to your questions are as follows.
1. All changes are not desirable. Desirable changes are those changes brought about by a person or nature that are useful to mankind and environment. Changes caused by natural calamities, rotting of fruits and vegetables etc. are not useful to mankind. These are therefore classified as undesirable changes.
2. Burning of paper is a chemical and irreversible change. On the other hand, tearing of paper is a physical and irreversible change. Let us understand why these are so. On burning, a paper gets converted to ash. Now, ash is a new substance formed and the formation of a new substance is a characteristic of chemical change. Also, the ash formed cannot be converted back to original paper. Hence, it is an irreversible change too. Now, consider the case of tearing. Tearing of paper converts the paper into bits of papers. No new substance is formed here, only the shape and size of the paper changes. Hence, it is a physical change. Also, the bits of paper cannot be converted back to original paper. So, it is an irreversible change.