The rate of diffusion within these entities can be quantified by the Thiele modulus.
The rate of diffusion within these entities can be quantified by the Thiele modulus. One type of these entities works by facilitating ion transfer between two phases and is exemplified by quaternary ammonium salts and crown ethers. "Sacrificial" varieties of these entities are used to regenerate other examples of them in their namesake (*) "cycles." The selectivity of these compounds can be increased by adding a poison. Whether they are heterogeneous or homogenous depends on whether they are in the same or a different phase from the reactants. For 10 points, name these compounds exemplified by enzymes, which lower the activation energy, thus speeding up reactions.
The rate of diffusion within these entities can be quantified by the Thiele modulus.
catalysts [accept more specific answers such as "phase-transfer catalysts"]