Question

Which of the following is a physical change? Explain with reason.

(a) Electrolysis of water gives hydrogen and oxygen.

(b) A bulb glows when electricty is passed through it.

Answer 1

Changes can be classified as physical and chemical changes

(a) Electrolysis of water gives hydrogen and oxygen is a chemical change, since

• The water changed into hydrogen and oxygen by breaking bonds.
• New substances like hydrogen and oxygen formed.
• Therefore, electrolysis of water gives hydrogen and oxygen is a chemical change.

(b) A bulb glows when electricity is passed through it, is a physical change, since

• Changes which involve physical properties like colour, appearance etc.., are called physical change.
• When the current pass through the filament, bulb glows and the chemical properties of the filament didn't change.
• Therefore, a bulb glows when electricity is passed through it, is a physical change.

Physical changes	Chemical changes
Changes which involve only physical properties like colour, appearance, etc.	Changes which involve only chemical properties like change in bonding, energy, etc.
Generally, no new substance formed here.	Generally, new substances formed.
No energy or heat change involved.	Generally involves energy or heat change.
Example: melting of ice	Examples: ripening of fruit