Chemicals and chemical changes

You have learnt about physical and chemical changes in the previous class. You know  that a change in which  no new substances are formed and which can generate be reversed by reversing the conditiond  is called a physical change. In physical changes only the properties likes shape size colous or state of the substance get changed. The common examples of.  physical  changes are melting of ice melting of wax boiling of water dissolution of sugar in water etc.

The changes in which two or more substances react to form new substance having different properties are called chemical changes or reactions. Chemical changes take place  around us all the time.  Burning fuel cooking food. Photosynthesis  etc. Are the examples of chemical changes or reactions . In this chapter we will study more about chemical changes.

                                  SUBSTANCE

Any material with a specific chemical composition is called substances.  There are two major types of substances pure substance and mixture.