science lesson number 13

a) A physical change is one which involves changes in the physical properties of a substance such as state, shape, size, and colour etc. No new substances are formed in a physical change. Also the original substance can generally be recovered again in a physical change i.e. most physical changes are reversible. For example,

 

Ice → Water → Steam (They are all water)

 

A chemical change is the one in which formation of one or more new substances takes place. The new substance formed has different chemical properties from that of the substance that formed it. Also the original material cannot be recovered easily i.e. it is an irreversible change. For example when lime is added to water, the temperature of water increases and water almost starts boiling. A substance called slaked lime is produced during this change. Hence, it is a chemical change. The following chemical equation can be used to represent the chemical change:

 

CaO + H2O → Ca (OH)2 + Energy

 

b) Changes which are repeated after regular intervals are called periodic changes. The occurrence of day and night and even the change of periods in your school are examples of periodic changes. Changes which do not take place periodically, such as freezing of water to form ice, are non-periodic changes.

Example: Respiration is non periodic change as it occurs in living organisms and it is affected by anatomical and physiological changes.

 

For remaining queries, we request you to post them in separate threads to have rapid assistance

from our experts.