regular solution

A regular solution is a mixture where molecules mix randomly, without preference for their neighbors based on chemical identity. This occurs when the molecules of the components are similar in size and lack strong orienting forces like dipoles or hydrogen bonding. The mixing process can be visualized using a lattice model, where the energy change depends on the interactions between different types of molecules.1

While regular solutions assume random mixing (S^E = 0), real solutions are often a combination of regular and athermal behaviors, meaning they are neither perfectly regular nor entirely athermal. Athermal solutions, in contrast, involve molecules of significantly different sizes, leading to a greater degree of disorder due to the increased configurations available to larger molecules in a solvent of smaller ones.2