Chemistry

Matter in Our Surroundings

Physical Changes

Those changes in which no new substances are formed,are called physical changes. In a physical change, the substances involved do not change their identity. They can be easily returned to their original form by some physical process. This means that physical changes can be easily reversed.The changes physical state size and shape of a substance are physical changes. Some common examples of physic changes are : Melting of ice (to form water);freezing of water (to form ice); Boiling of water (to form steam) Condensation of steam (to form water); Making a solution ; Glowing of an electric bulb,Breaking of a glass tumbler. These physical changes are discussed on the next page.
(i) When ice is heated, it melts to form water. Though ice and water look different, they are both made of water molecules. Thus, no new chemical substance is formed during the melting of ice. So,the melting of ice to form water is a physical change.When water is cooled (as in a refrigerator), then water solidifies to form ice. This is called freezing of water.The freezing of water to form ice is also a physical change.
(ii) When water is heated,it boils to form steam.Though steam and water look different, they are both made of water molecules. Thus, no new chemical substance is formed during the boiling of water. So,the boiling of water to form steam is a physical change.When steam is cooled,it condenses (liquefies) to form water.The condensation of steam to form water is also a physical change.
(iii) When an electric bulb is switched on,an electric current passes through its filament. The filament of bulb becomes white hot and glows to give light. When the current is switched off, the filament returns to its normal condition and the bulb stops glowing. No new substance is formed in the bulb during this process. So,the glowing of an electric bulb is a physical change.
(iv) We take water in a china dish and dissolve some common salt in it.The salt disappears in water and forms a salt solution. So, a change has taken place in making salt solution. Let us now heat this china dish containing salt solution on a burner till all the water evaporates. A white powder is left behind in the china dish. If we taste this white powder, we will find that it is common salt. It is the same common salt which we had dissolved in water earlier. This means that no new chemical substance has been formed by dissolving common salt in water to make salt solution.Thus,making of a solution is a physical change.
(v) When a glass tumbler breaks, it forms many pieces. Each broken piece of glass tumbler is still glass.So, during the breaking of a glass tumbler, only the size and shape of glass has changed but no new substance has been formed. So,the breaking of a glass tumbler is a physical change.The physical changes are temporary changes which can be reversed easily to form the original substance. For example, the melting of ice to form water is a temporary change. We can reverse this physical change easily by cooling water to form the original substance, ice.
Some more examples of physical changes are : Melting of wax ; Melting of butter in a pan ; Melting of glass ; Dissolving common salt in water ; Making a fruit salad from raw fruits; Mixing of iron filings and sand ; Sublimation of a solid ; Making of soda water by dissolving carbon dioxide in water ; Formation of clouds ; Breaking of a piece of chalk ; Stretching of a rubber band ; Cutting or tearing a piece of paper ;Tearing of cloth ; and Rotation of a fan.

Notes

Matter in Our Surroundings - Notes

1. 3. Non-Metals are Bad Conductors of Heat and Electricity.