* Temperature Increase: The heat released indicates a chemical reaction is taking place. This is because the energy stored in the chemical bonds of the reactants (hydrochloric acid and sodium hydroxide) is being released as heat when they form new bonds to create products.

* No Visible Change: While there might not be a dramatic color change or gas formation, the reaction is still happening. The chemical reaction creates salt (sodium chloride) and water.

The reaction equation:

HCl (hydrochloric acid) + NaOH (sodium hydroxide) → NaCl (sodium chloride) + H₂O (water) + heat

Key Points:

* Chemical changes involve the formation of new substances with different chemical properties.

* Physical changes alter the form or appearance of a substance but not its chemical composition.

* In this case, the temperature increase and the formation of new substances (salt and water) indicate a chemical change.