Il sale si dissolve in acqua. È un cambiamento chimico o fisico?
Risposta:
This question is bound to provoke controversy; it certainly has before. The dissolution of sodium chloride in water is clearly a chemical change.
Spiegazione:
Please, before you say that such dissolution is reversible, read the entirety of this old thread. As always, chemical change is characterized by the formation of new substances and the making and breaking of strong chemical bonds.
And for...
#NaCl(s) stackrel(H_2O)rightleftharpoonsNa^+ + Cl^(-)#
The strong ionic interaction between #Na^+# e #Cl^(-)# is BROKEN, and new ion-dipole bonds are formed between the water solvent, and the individual ions...i.e. we might write #Na^+# or #NaCl(aq)#...IN SOLUTION the individual species are likely #[Na{(OH)_2}_6]^+# etc., ion-dipole complexes that are manifestly distinct from the starting material. That this reaction is reversible DOES NOT differentiate....in that MANY chemical reactions, including all equilibrium reactions, are reversible, including this one:
#1/2H_2(g) + 1/2Cl_2(g) rightleftharpoonsHCl(g)#
And this one is unambiguously an example of chemical change. Below undergraduate level, many teachers would maintain that salt dissolution is physical. They are mistaken.