Physical and chemical changes

PHYSICAL AND CHEMICAL CHANGES

Physical Changes:

•    Those changes in which no new substance is formed are called physical changes.

•    During physical changes, the properties of a substance remain the same.

•    Many times they are temporary and can be reversed. Melting of ice is one such change.

•    There are some changes which are physical but irreversible. For example:

      (a) Plucking of leaves

      (b) Tearing of paper

      (c) Breaking of glass

Chemical Changes:

•    Those changes in which a new substance is formed, which have different chemical properties, are called chemical changes.

•    Cooking of food, growth in plants and animals, burning of substances are chemical changes as entirely new substances are formed.

•    Burning of a candle wax releases carbon dioxide and water vapour (new substances).

Example:

Cooking of food:

•    On cooking, the colour, hardness and appearance of food changes.

•    Cooking of food is a chemical change.

Ripening of fruit:

•    Turning of a raw, green mango into a ripe yellow mango is also a chemical change.

Difference between Physical and chemical change: