Here's why:
* Chemical changes involve the formation of new substances with different properties. This means the atoms within the original substances are rearranged to form new bonds and create entirely new molecules.
* The original substances are consumed and transformed. They no longer exist in their original form.
* Chemical changes are irreversible without further chemical reactions. You can't simply "undo" a chemical change by reversing the process.
Example:
Burning wood is a chemical change. The wood (cellulose) reacts with oxygen to form ash, carbon dioxide, and water. The wood is gone, and new substances are created. You can't get the wood back by simply combining the ash, carbon dioxide, and water.
Key Point: The core principle of chemical change is the creation of new substances with different properties. The original substances are not simply rearranged; they are transformed into something entirely new.
