* New substances are formed: Strontium (Sr) reacts vigorously with water (H₂O) to produce strontium hydroxide (Sr(OH)₂) and hydrogen gas (H₂). This is evident by the formation of bubbles (hydrogen gas) and the release of heat.

* Irreversible reaction: The reaction is not easily reversible. You can't simply separate the strontium hydroxide and hydrogen back into strontium and water.

* Chemical bonds are broken and formed: The original chemical bonds in strontium and water are broken, and new bonds are formed to create strontium hydroxide and hydrogen gas.

In contrast, a physical change involves a change in the form or appearance of a substance, but not its chemical composition. Examples of physical changes include melting ice, boiling water, or cutting paper.