Is Dissolving a Chemical Change?
A chemical change involves the formation of new substances through chemical reactions. The newly formed products have chemical properties that differ from the starting substances. A physical change does not involve any chemical reaction. It only results in a change in appearances like size and shape. Dissolving a solid in a liquid is a physical and chemical change depending on the solute and the solvent [1-4].
Consider salt and water. When common salt or sodium chloride (NaCl) dissolves in water, it dissociates into sodium ions (Na+) and chloride ions (Cl-‑). The following chemical reaction occurs.
NaCl (s) → Na+ (aq.) + Cl– (aq.)
New ions are formed that differ from the original compound. The same type of reaction occurs when an ionic substance is dissolved in water. Since the process involves the formation of new species through a chemical reaction, dissolving salt in water is a chemical change.
On the other hand, consider dissolving sugar in coffee. Sugar, which consists of hydrogen and carbon atoms, dissolves entirely in coffee but does not break down into new species. The sugar molecules disperse completely in coffee but do not change their chemical identity. Therefore, dissolving sugar in coffee or water is not a chemical change. Instead, it is a physical change.