Science Answer The Following Questions In Short.[2 Marks Each]

Examples of physical changes:Tearing of sheet of paper into pieces, melting of ice, change of water into steam, breaking of glass tumbler, glowing of electric bulb, dissolution of sugar or salt in water.
Examples of chemical changes:
Burning of paper, wood, candle, etc., formation of curd from milk, cooking of food, rusting of iron and mixing of vinegar with baking soda, electrolysis of water.

Changes that can be reversed are called reversible changes. Some examples are as follows:

1. Melting of wax.
2. Folding of a paper.
3. Knitting of a sweater.
4. Inflating of a tyre.

1. Physical change, irreversible change.
2. Periodic change, irreversible change.
3. Irreversible change,
4. Irreversible change, chemical change.
5. Irreversible change.

She can easily open the bottle because of expansion of metal cap (increase in size) due to heating.
Note: When a metal object is heated, it increases in size and when the hot object is cooled, it decreases in size and comes back to the original size.

Reversible and irreversible changes:
Reversible changes: The changes which can be brought back to its original form are known as reversible changes. For example, melting of wax and stretching of a rubber band.
Irreversible changes: The changes in which the matter cannot be brought back to its original state are known as irreversible changes. For example, burning of paper changes it into ash and smoke. Paper cannot be obtained back from ash and smoke.

Solute is the substance that is dissolved in the solvent to form a solution. For example, in a sugar solution, sugar is the solute and water is the solvent.

It is a physical change. Water after evaporation goes into the air, and form clouds by condensation process, so the water get back to the earth by precipitation.

Its length will be reduced.

No, the change in the length of the candle cannot be reversed. Yes, on heating the wax in a pan, its change into liquid form can be reversed.

In this case, the changes cannot be reversed. This is because the cement that hardens up after getting wet cannot be obtained back.

The metal rim is always made slightly smaller than the wooden wheel. The metal rim is heated; on heating, the rim expands and fits onto the wheel. Cold water is then poured over the rim. Due to cooling, rim contracts and fits tightly over the wheel.

1. Drying the wet clothes.
2. Liquid water into water vapour.

1. When ice is kept outside the freezer, it melts.
2. When alcohol is put on the back of palm, it evaporates.

We can get the paper on paper recycling but it is not the same original paper that we get. The colour and texture of the paper change.

Physical change: Physical change is a temporary change in which chemical composition of the substance does not change and no new substance is formed.
During a physical change, only the physical properties of a substance change.
It is a reversible change. For example, melting of ice, during this change, the water changes from its solid form to liquid form. It can be solidified again.The water remains water in both the cases.
Chemical change: A chemical change is a permanent change in which not .
only the physical properties but chemical properties also change. It is an irreversible change. For example, formation of curd from milk, rusting of iron, etc.

A small quantity of curd is added to warm milk. The milk is stirred and is set aside undisturbed for a few hours at a warm place. In a few hours, the milk changes into curd.
Curd formed from milk cannot be changed into milk again. So, this is an irreversible change.

Iron blade of tools has a ring in which the wooden handle is fixed. Normally the ring is slightly smaller in size than wooden handle. To fix handle ring is heated and it expands. Now handle easily fits into the ring. When ring cools down it contracts and fits into handle.

Changes that cannot be reversed are called irreversible changes. Some examples are as follows:

1. Milk into curd.
2. Burning of wood.
3. Ripening of fruits.
4. Digestion of food.

The softening of iron on heating to red hot stage is a reversible change. And when the hot iron is cooled, it becomes hard again.

• Melting of ice: During this change, the water changes from its solid form to liquid form. It can be solidified again. The water remains water in both cases, hence reversible.
• Glowing of an electric bulb: During this change, electricity is passed through the tungston filament which becomes white hot and glows, but when the switch is off, the filament returns to its original shape and condition, hence totally reversible.

Metal rim is made slightly smaller than the wooden wheel. On heating rim expands and fits into wheel. Cold water is then poured over rim, which contracts and fits tightly onto the wheel.

Many changes are taking place around us on their own. For example:

1. Ripening of crops in the fields.
2. Leaves fall from trees.
3. Flowers bloom and then wither away.
4. Growing of hair and nail.