The discussion centers on the physical mechanism behind the fuming of oleum, particularly how dissolved SO3 reacts exothermically with air humidity. It is noted that the reaction occurs at the liquid's surface, generating heat that influences the surrounding environment. The condensation of mist above the surface is attributed to the high partial pressure of SO3, which leads to condensation in the presence of water vapor. This process occurs in the gas phase above the oleum, rather than the sulfuric acid dissolving in the solution. The conversation also references the chemistry principle of "acid to water, never water to acid," highlighting the differences in physical processes between adding water to acid and the fuming of oleum. Overall, the fuming phenomenon is explained through the interplay of reaction heat, vaporization, and condensation dynamics.
