Here's why:

* Chemical properties describe how a substance reacts with other substances or how it changes its composition. These changes involve the formation of new substances with different properties.

* Chemical changes are processes that result in the formation of new substances.

For example:

* Flammability is a chemical property. You can only observe if a substance is flammable by trying to burn it (a chemical change).

* Reactivity with acids is another chemical property. You can only observe this by reacting the substance with an acid, which will cause a chemical change.

In contrast, physical properties can be observed without changing the composition of the substance. These properties include things like color, density, melting point, etc.