Final answer:
The Brønsted-Lowry model defines an acid as a proton donor and a base as a proton acceptor; it extends the definition of acids and bases beyond the limited Arrhenius model by focusing on proton transfer, as seen in the reaction between ammonia and water.
Step-by-step explanation:
The Brønsted-Lowry model defines an acid as a substance that can donate a hydrogen ion (proton) and a base as a substance that can accept a hydrogen ion. This definition is more general than the Arrhenius definition, which is limited to acids and bases in aqueous solutions. The Brønsted-Lowry model extends beyond just water as a solvent and includes a wider variety of acid-base reactions. For example, in the reaction of ammonia and water, ammonia acts as a Brønsted-Lowry base by accepting a hydrogen ion from water, which acts as a Brønsted-Lowry acid resulting in the formation of ammonium and hydroxide ions:
NH3(aq) + H2O(l) ⇒ NH4+(aq) + OH−(aq)
In this equation, water donates a proton to ammonia, illustrating the concept of proton transfer central to the Brønsted-Lowry definition.