* Chemical Reaction: Calcium (Ca) reacts with water (H₂O) to form calcium hydroxide (Ca(OH)₂) and hydrogen gas (H₂). This is a chemical reaction because new substances are formed with different properties.

* Formation of New Substances: The original calcium metal and water molecules are no longer present after the reaction. They have been transformed into calcium hydroxide and hydrogen gas.

* Evidence of Chemical Change: The reaction produces a noticeable release of heat (exothermic reaction), and bubbles of hydrogen gas are observed.

The chemical equation for this reaction is:

Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

Key takeaway: Dissolving calcium in water is not just a physical change where the calcium simply disperses. It involves a chemical reaction that produces new substances, indicating a chemical change.