Describes the macroscopic process of the swelling of clay by adding water, and the corresponding microscopic process of water molecules entering the spacings between clay crystals. Discusses how the Bragg equation can be used together with other physical data to calculate these spacings. (MLH)

This exercise, suitable for an advanced undergraduate physical chemistry lab, examines the detailed theoretical description of a chemical reaction. Mathematical techniques of moderate complexity serve to introduce some aspects of theoretical chemistry. (Author/TS)