Thomas Graham discovered the law that bears his name while studying gas diffusion into air and other gases. He also found that the same relationship held with gas effusion, the movement of gases through a pinhole into a vacuum. Modern understanding of diffusion and effusion is based on kinetic-molecular theory, and it is generally accepted that…

The hydrogenation of alkenes by heterogeneous catalysts has been studied for 80 years. The foundational mechanism was proposed by Horiuti and Polanyi in 1934 and consists of three steps: (i) alkene adsorption on the surface of the hydrogenated metal catalyst, (ii) hydrogen migration to the beta-carbon of the alkene with formation of a delta-bond…

In these two classroom demonstrations, students observe the reaction between H[subscript 2] gas and Pd foil. In the first demonstration, hydrogen and palladium combine within one minute at 1 atm and room temperature to yield the non-stoichiometric, interstitial hydride with formula close to the maximum known value, PdH[subscript 0.7]. In the…