Chemical changes Study Guide

Acids can be classified as strong or weak based on their degree of dissociation into ions when dissolved in water. A strong acid completely dissociates in aqueous solution, meaning all its molecules break apart to release hydrogen ions (H⁺). This results in a high concentration of H⁺ ions. Conversely, a weak acid only partially dissociates in aqueous solution. Most of its molecules remain intact, with only a small fraction releasing H⁺ ions. This leads to a lower concentration of H⁺ ions compared to a strong acid of the same concentration. The dissociation of a weak acid is a reversible process, establishing an equilibrium between the undissociated acid molecules and their dissociated ions.

In electrolysis, non-spontaneous chemical reactions are driven by electrical energy using electrodes in an electrolyte. At the cathode (negative electrode), cations (positive ions) gain electrons—this is called reduction. At the anode (positive electrode), anions (negative ions) lose electrons—this is called oxidation. Each electrode process can be described by a half-equation that shows the electron transfer. It is essential to balance both atoms and charges in these half-equations. Accurate half-equations allow us to track what happens to ions as they change to neutral atoms, molecules, or different ions during the process.