To make a solution of salt water two forms of a mixture are formed - heterogeneous and geneous mixtures.?

The heterogeneous mixture allows you to identify the substances (for example, if you mix salt with water , and insufficiently stir it whereby you can see both salt particles floating in water ) that are added. The geneous mixture makes it that you cannot identiffy the substances (ex, salt completely mixed with water) that are added. In both cases, we state that it's a physical change. Question: How is it when you write out the chemical formula H20 (water) + NaCl(salt) you get NaOH (sodium hydroxide) + HCl (hydrochloric acid) which appears like a chemical change. Please explain.