A vessel of volume V is divided into two identical parts containing different gases by two partitions. The partitions are permeable only to "their" gas from the part of the vessel that each of them initially separates. Under the influence of gases, the partitions move up to the walls of the vessel. Find the entropy increment in this motion if the initial gas pressure is P and the temperature is T. Why is such a process impossible if the gases on both sides are the same or it is impossible to distinguish one gas from another experimentally (for example, in the last century it was impossible to distinguish isotopes)?