What is a chemical change? Why do physical properties change?
Why do chemical properties change?

1.Chemical changes occur when a substance combines with another to form a new substance
2. A physical change takes place without any changes in molecular composition
3. When a substance goes under a chemical reaction, the properties will change

Chemical change: Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions.

A physical change takes place without any changes in molecular composition. The same element or compound is present before and after the change. The same molecule is present through out the changes. Physical changes are related to physical properties since some measurements require that changes be made.

When a substance goes under a chemical reaction, the properties will change drastically, resulting in chemical change. ... Chemical properties can be contrasted with physical properties, which can be discerned without changing the substance's structure.