Question

Give one example in each case: (2)

a. A change that occurs on heating, but can be reversed.

b. A change that occurs on mixing two substances, but cannot be reversed.​

Answer 1

A) On heating an ice or keeping it in a room temperature, it converts into water that is liquid. and on again freezing it it converts into ice that is solid form.

B) On burning camphor, ie by the process of sublimation, it is converted into gaseous form and it cannot be reversed after being converted into gas.

Answer 2

Answer:

a.)

Reversible change:

A change is said to be reversible when the opposite change can be brought about by reversing the condition.

Example:

• A solid melts on being heated and the melt solidifies (that is freezes) on being cooled. So, the melting of solid on being heated is reversible change.

• The vaporization of water on being heated and the condensation of vaporization on being cooled, it is a reversible change.

• The heating and cooling of coil of an electric heater, when the heater is switched on and off respectively a reversible changes.

b.)

Irreversible change:

A change is said to be irreversible when the opposite change cannot be brought about by reversing the condition.

Example:

• Lead nitrate when mixed with potassium iodide reacts to make lead iodide. It is a chemical change and irreversible.

• Cement when mixed with water cannot be reversed by reversing the condition.

• Sodium chloride and silver nitrite when mixed with each other in molten state, react to form the precipitate of silver chloride and sodium nitrate.

• Oxalic acid crystals when mixed with sodium carbonate react in water solution and it is a irreversible change.

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