Final answer:
Acids react in water because water can break apart the acid into hydrogen ions (or hydronium ions when they associate with water molecules) and other ions. This dissociation process is due to water's solvent properties and polar nature. Both strong acids like HCl and weak acids undergo this process, with strong acids being nearly 100% efficient in their reaction.
Step-by-step explanation:
The best statement that explains why acids only react when placed in water is: This is because water can break apart the acid into hydrogen ions and salt. The unique properties of water as a solvent allow it to facilitate the ionization of acids. In water, an acid like hydrogen chloride (HCl) dissolves to yield hydronium ions and anions (such as Cl-) in a process called dissociation. When HCl is dissolved in water, a chemical reaction occurs where H+ ions are transferred from HCl molecules to water molecules, forming H3O+ (hydronium ions).
Acids and bases behave differently in water due to its highly polar nature. This polarity allows water molecules to act as an acid (proton donor) or a base (proton acceptor). For instance, a strong acid like HCl is nearly 100% efficient in reacting with water, while weak acids only partially ionize, producing fewer hydronium ions and maintaining more of their original molecules intact in solution.
Overall, water's ability to act as a solvent and its polar structure are fundamental for the reaction of acids, allowing them to dissociate into their respective ions and react to form various products, hence engaging in acid-base reactions.