Mixing of Ideal Materials At Constant Temperature and Pressure
In ideal materials, intermolecular forces are the same between every pair of molecular kinds, so that a molecule feels no difference between itself and its molecular neighbours. This is the reference case against which are examined corresponding mixings of non-ideal materials.
For example, two ideal gases, at the same temperature and pressure, are initially separated by a dividing partition.
Upon removal of the dividing partition, they expand into a final common volume (the sum of the two initial volumes), and the entropy of mixing is given by
- .
where is the gas constant, the total number of moles and the mole fraction of component which initially occupies volume . After the removal of the partition, the moles of component may explore the combined volume, which causes an entropy increase equal to for each component gas.
In this case, the increase in entropy is due entirely to the irreversible processes of expansion of the two gases, and involves no heat or work flow between the system and its surroundings.
Read more about this topic: Entropy Of Mixing
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