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what is the difference between physical and chemical changes ?
Chemical change is any change that results in the formation of new chemical substances. At the molecular level, chemical change involves making or breaking of bonds between atoms. These changes are chemical:

   1. iron rusting (iron oxide forms)
   2. gasoline burning (water vapor and carbon dioxide form)
   3. eggs cooking (fluid protein molecules uncoil and crosslink to form a network)

 Physical change rearranges molecules but doesn't affect their internal structures. Some examples of physical change are:

    1. whipping egg whites (air is forced into the fluid, but no new substance is produced)
    2. magnetizing a compass needle (there is realignment of groups ("domains") of iron atoms, but no real change within the iron atoms themselves).


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