Ann is studying acid base neutralization reactions and mixes sodium hydroxide and hydrochloric acid. The reactants were clear, colorless solution and mixing them produces a clear, colorless final solution and the beaker becomes warm. She knows this reaction forms liquid water and an aqueous salt based on the neutralization rules as shown by the chemical equation. What physical evidence indicates that there has been a chemical reaction? NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)