In this problem you will model the mixing energy of a mixture in a relatively simple way, in order to relate the existence of a solubility gap to molecular behavior. Consider a mixture of A and B molecules that is ideal in every way but one: The potential energy due to the interaction of neighboring molecules depends upon whether the molecules are like or unlike. Let n be the average number of nearest neighbors of any given molecule (perhaps 6 or 8 or 10). Let Uo be the average potential energy associated with the interaction between neighboring molecules that are the same (A-A or B-B), and let UAB be the potential energy associated with the interaction of a neighboring unlike pair (A-B). There are no interactions beyond the range of the nearest neighbors; the values of Uo and UAB are independent of the amounts of A and B; and the entropy of mixing is the same as for an ideal solution. Show that when the system is unmixed, the total potential energy due to all neighbor-neighbor interactions is 1/2 Nnuo.
In this problem you will model the mixing energy of a mixture in a relatively simple way, in order to relate the existence of a solubility gap to molecular behavior. Consider a mixture of A and B molecules that is ideal in every way but one: The potential energy due to the interaction of neighboring molecules depends upon whether the molecules are like or unlike. Let n be the average number of nearest neighbors of any given molecule (perhaps 6 or 8 or 10). Let Uo be the average potential energy associated with the interaction between neighboring molecules that are the same (A-A or B-B), and let UAB be the potential energy associated with the interaction of a neighboring unlike pair (A-B). There are no interactions beyond the range of the nearest neighbors; the values of Uo and UAB are independent of the amounts of A and B; and the entropy of mixing is the same as for an ideal solution.
Show that when the system is unmixed, the total potential energy due to all neighbor-neighbor interactions is 1/2 Nnuo.
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