Question

define :

chemical changes in 100 words
physical changes in 100
words.

Answer 1

chemical changes :

the nature of original substance would be change. if new substances are formed with properties completely unlike those of the original substances, we can say a chemical change take place.

examples :

coal is burnt.
food get digested in our body.
iron nail is exposed to humid atmosphere for a long time.
we respire.
milk is converted into curd.
water is added to quick lime.
crackers are burnt.

physical change :

this change is quite opposite to the chemical change.
the nature of original substance would be remained same.the properties are likely same.it is an temporary change.

examples :

water converts into ice
ice converts into water
gas converts into water (rain)
water converts into gas(clouds formation)

Answer 2

Changes which are not reversible are chemical changes. A new product is formed. There is evolution of gas. There is change in colour. For eg burning of oil. Changes which are reversible. No new product is formed. There is no evolution of gas and thus no colour change are known as physical changes. These changes can sometimes not reversed. Such as tearing of paper