Definition for View source for Comparison of Physical and Chemical Changes

A substance is said to undergo a physical change when it changes from one state to another. The changes of water when it is boiled or frozen are examples of physical changes. When water is heated until it boils, bubbles of gas rise through the hot liquid. We know this gas as steam. If the steam that is produced when water is boiled is cooled down to room temperature, a liquid (i.e. water) is formed. If water is cooled much below room temperature, a solid known as ice is formed. 

Whenever a process takes place with the production of one or more new materials, the process itself is called a chemical change or a chemical reaction. This process takes place within a chemical system. In a chemical reaction, the initial materials called reactants, and these are replaced as a result of the chemical change by a new set of materials called products. In order to distinguish between a physical and chemical change, it is necessary to find out if a new substance has been formed. If a new substance has been formed in the change, a chemical change has taken place. 

As matter may undergo changes which may be either physical changes or chemical changes, the following table indicates the differences between physical and chemical changes. 

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'''Characteristics of a physical change''' 

#This may be a change from solid to liquid to gas, or solid to gas no new kind of matter being formed. 
#This change of state is reversible, e.g. gas to liquid to solid. 
#No change in weight.

'''Characteristics of a chemical change''' 

#A new type of matter is formed. 
#This change is not easily reversible. 
#The weight of each reacting substance changes, although the total weight remains unchanged.