7. Define the following.
a. Reversible change
b. Physical change
c. Irreversible change
d. Chemical change
G Answer the following questions in detail
1. Give examples to explain the difference between the changes that can be reversed and those that cannot be reversed.
2. Write any two characteristics of irreversible changes.
3. What are physical changes? Give two examples.
4. Why is sharpening of a pencil considered to be a physical change?
5. Name the new materials formed when an incense stick is burnt.
6. Burning of paper is a chemical change. Justify.
7. Differentiate between:
a. reversible and irreversible changes
b. physical and chemical changes
c. evaporation and condensation
d. expansion and contraction
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Verified answer
7.
a. A reversible change is a change that can be undone or reversed. If you can get back the substances you started the reaction with, that's a reversible reaction. ... Examples of reversible reactions include dissolving, evaporation, melting and freezing.
b. Physical changes are changes affecting the form of a chemical substance, but not its chemical composition. ... Examples of physical properties include melting, transition to a gas, change of strength, change of durability, changes to crystal form, textural change, shape, size, color, volume and density.
c. An irreversible change is when something cannot be changed back to its original form.
d. Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions.
G
1. Melting of ice is a reversible change. ... When ice cubes are kept at room temperature, they turn into water after some time. On the other hand, burning of a piece of paper is an irreversible change.
2. A change which cannot happen backward, that is, it cannot be reversed is called an irreversible change. When you burn a piece of paper, it turns to ash. It cannot become paper again. Your height cannot decrease.
3. Changes in the size or form of matter are examples of physical change. Physical changes include transitions from one state to another, such as from solid to liquid or liquid to gas. Cutting, bending, dissolving, freezing, boiling, and melting are some of the processes that create physical changes.
4. When you sharpen your pencil, you have only caused a physical change. The sharpener has cut off some of the wood and maybe also some of the graphite, but the atoms of the wood and graphite have not changed chemically. ... This is only a physical change.
5. Ash is formed while burning incense stick.
6. Burning of paper is not a physical change. It is chemical change as ash is formed in the process which is new compound and oxides of carbon are also released during the process.
7. For No. 7 answers refer the above attachment