What is the definition of an acid according to the Brønsted-Lowry theory?

The Brønsted-Lowry theory defines an acid as a proton donor. According to this theory, acids are substances that can donate a hydrogen ion (H⁺) to another substance (the base), which accepts that proton. This framework emphasizes the transfer of protons during acid-base reactions rather than focusing solely on the presence of hydroxide ions or the release of hydrogen ions in solution.

In this context, an acid facilitates the process of forming conjugate bases when it donates a proton, thus playing a crucial role in acid-base chemistry. The proton donor concept aligns with various chemical reactions, including those in aqueous solutions and organic chemistry, where hydrogen ions are fundamental to the behavior of acids. Understanding this definition is essential for grasping further concepts in acid-base chemistry, as it lays the groundwork for studying how different acids react in various chemical environments.