Question

why a physical change can not alter the chemical properties of a substance

Answer 1

The chemical change as hydrogen peroxide (H2O2) becomes watercannot be seen since both liquids are clear. ... Those bubbles are evidence of the chemical changes. Melting a sugar cube is a physical change because thesubstance is still sugar. Burning a sugar cube is a chemical change

Answer 2

Physical change refers to factors like change in temp., color or shape which is the result of of the chemical properties of substance. But when we talk about the chemical properties it is due the the atoms and molecules involved, the interaction between them which will always be same for a perticular substance.

for example a diamond chemical properties arise due to its str. and C molecules involved. Even if we cut it down or polish it, it will not turn into gold.