Question

Which of the following is not a physical change?
A. Boiling of water to give water vapor
B. Melting of ice to give water
C. Dissolution of salt in water
D. Combustion of liquefied petroleum gas (LPG)

Answer 1

Hint: Changes in energy can be easily noted by a particular chemical change or physical change. Many changes happen naturally like in an environment for example evaporation of water, condensation, rainfall etc. During some chemical reactions the old bonds get broken and new bonds are formed.

Complete Solution :
- To find out which one is not physical change we have to go through the concept of what is physical change. During the physical change arrangement of the molecules is disturbed due to which they change their state. Molecular composition remains the same during this change and no new products are formed. In physical change energy changes is also nil. The energy required to bring a physical change is generally equal to the amount of energy required to reverse the change so we can say that there is no change in energy. The changes are reversible and temporary in nature and the reaction gets reversed if the cause of producing the change is removed. During the physical change the mass of the substance remains the same. Only energy is added or removed during the physical change and mass is not involved in a physical change.
- As from the discussion we can consider that a physical change involves only change in physical state whereas a chemical change results in the formation of new substances. Boiling of water, melting of ice and dissolution of salt are physical changes as no new products are formed.
So, the correct answer is “Option D”.

Note: The change in which the molecular composition is completely changed and a new product is formed known as the chemical change. Chemical changes create a new product and changes in this are irreversible and permanent in nature.