* Chemical Changes Involve New Substances: When a substance reacts with acid, it undergoes a chemical change. This means the original substance breaks down and forms new substances with different properties. For example, when a metal reacts with acid, it may produce hydrogen gas and a salt.

* Chemical Reactions are Irreversible: Chemical changes are generally irreversible. The new substances formed cannot be easily converted back to the original substances.

* Changes in Properties: Chemical changes are accompanied by changes in physical properties, such as color, odor, taste, and state of matter.

Examples of Chemical Changes Involving Acids:

* Metal + Acid: Metals react with acids to produce hydrogen gas and a salt.

* Carbonate + Acid: Carbonates react with acids to produce carbon dioxide gas, water, and a salt.

* Base + Acid: Bases react with acids in a neutralization reaction to form water and a salt.

In summary: The ability to react with acid indicates a substance's potential to undergo a chemical change, forming new substances with different properties.