Suppose the gases are completely mixed, so the system has maximum entropy as it is in the macrostate with the greatest number of microstates. It is possible is it not that the gases could separate. This will have fewer microstates and so a lower entropy. Although this is unlikely, it is possible. Hence entropy can decrease in a closed system. | Suppose the gases are completely mixed, so the system has maximum entropy as it is in the macrostate with the greatest number of microstates. It is possible is it not that the gases could separate. This will have fewer microstates and so a lower entropy. Although this is unlikely, it is possible. Hence entropy can decrease in a closed system. |