Question

(a) What is a physical change ? Give two examples of physical changes.
(b) What is a chemical change ? Give two examples of chemical changes.

Answer 1

Answer:

Chemical Changes: Chemical changes take place on the molecular level.

A chemical change produces a new substance. Examples of chemical

changes include combustion (burning), cooking an egg, rusting of an iron

pan, and mixing hydrochloric acid and sodium hydroxide to make salt and

water.

Examples of Chemical Changes

1.burning wood

2. mixing acid and base

3.digesting food

Physical Changes: Physical changes are concerned with energy and

states of matter. A physical change does not produce a new substance.

Changes in state or phase (melting, freezing, vaporization, condensation,

sublimation) are physical changes. Examples of physical changes include

crushing a can, melting an ice cube, and breaking a bottle.

Examples of Physical Changes

1.crumpling a sheet of paper

2.dissolving sugar in water

3.melting an ice cube

4.casting silver in a mold

5.breaking a bottle

Answer 2

Answer:

Physical changes :-

Those changes in which only physical properties of the substance change but no new substances are formed are called physical changes. Physical Changes temporary and hence can be reversed.

Example:-

● Melting of ice to form water and freezing of water to form ice.

● Boiling of water to form steam and condensation of steam to form water.

● Glowing of a bulb

● Breaking of glass tumbler.( this cannot be reversed but still considered as a physical changes because no new substances are formed )

● Tearing of Paper .

Chemical changes :-

Those changes in which new substances are formed are called chemical changes. Chemical Changes are permanent and hence cannot be reversible.

Example:-

● Burning of magnesium ribbon .

( 2Mg + O2 -> 2MgO)

● Burning of Hydrogen in air .

( 2H2 + O2 -> 2H2O)

● Rusting of Iron

( 2Fe + O2 -> 2FeO)

● Formation iron sulphide from iron and sulphate.

● Burning of Paper .

Explanation: