Identify the Brønsted–Lowry acid–base pairs in each of the following equations:
b. NH₄⁺(aq) + H₂O(l) ⇄ NH₃(aq) + H₃O⁺(aq)

Verified step by step guidance

1. Step 1: Recall the Brønsted–Lowry definition of acids and bases. A Brønsted–Lowry acid is a substance that donates a proton (H⁺), while a Brønsted–Lowry base is a substance that accepts a proton.
2. Step 2: Analyze the reactants and products in the equation: NH₄⁺(aq) + H₂O(l) ⇄ NH₃(aq) + H₃O⁺(aq). Identify which species donates a proton and which species accepts a proton.
3. Step 3: Observe that NH₄⁺ (ammonium ion) donates a proton (H⁺) to H₂O (water), forming NH₃ (ammonia) and H₃O⁺ (hydronium ion). This makes NH₄⁺ the Brønsted–Lowry acid and NH₃ its conjugate base.
4. Step 4: Recognize that H₂O accepts the proton from NH₄⁺, forming H₃O⁺. This makes H₂O the Brønsted–Lowry base and H₃O⁺ its conjugate acid.
5. Step 5: Conclude that the Brønsted–Lowry acid–base pairs are: (1) NH₄⁺ (acid) and NH₃ (conjugate base), and (2) H₂O (base) and H₃O⁺ (conjugate acid).

Key Concepts

Brønsted–Lowry Theory

The Brønsted–Lowry theory defines acids as proton donors and bases as proton acceptors. This framework allows for a broader understanding of acid-base reactions beyond just the presence of hydroxide or hydronium ions. In this theory, the transfer of protons (H⁺ ions) between species is the central focus, making it essential for analyzing chemical equations involving acids and bases.

Acid-Base Pairs

An acid-base pair consists of two species that differ by the presence or absence of a proton. In a Brønsted–Lowry context, the acid in the pair donates a proton, while the base accepts it. Identifying these pairs in a reaction helps to clarify the roles of different species and the direction of proton transfer, which is crucial for understanding the dynamics of the reaction.

Equilibrium in Acid-Base Reactions

Acid-base reactions often reach a state of equilibrium, where the rates of the forward and reverse reactions are equal. This concept is important for understanding how the concentrations of reactants and products change over time. In the given equation, recognizing the equilibrium allows for the identification of the acid-base pairs and the direction of proton transfer, which is vital for predicting the behavior of the system.