Resumen de Improving Students’ Understanding of the Connections between the Concepts of Real-Gas Mixtures, Gas Ideal-Solutions, and Perfect-Gas Mixtures
Romain Privat, Jean Noël Jaubert, Edouard Moine
In many textbooks of chemical-engineering thermodynamics, a gas mixture obeying the fundamental law pVm = RT is most often called ideal-gas mixture (in some rare cases, the term perfect-gas mixture can be found). These textbooks also define the fundamental concept of ideal solution which in theory, can be applied indifferently to liquid or gas mixtures but in practice, is nearly always introduced through the instance of liquid solutions. Undergraduate students are thus faced with different theoretical solution models that are all named “ideal” which can be a source of confusion. It is indeed often observed either that the connections between the concepts of perfect gas and ideal solution are missed by undergraduate students, or that they do not make any distinction between the concepts of gaseous ideal-solutions and perfect-gas mixtures. In this article, a simple example is proposed to pedagogically clarify all the misconceptions inherited from the multiple definitions of ideal mixtures and to explicate the connections between the various concepts in terms of molecular interactions. In particular, it is illustrated how an ideal solution (liquid or gas) can be derived from a real mixture (liquid or gas) by imposing constraints on molecular interactions. Similarly, it is shown how a perfect-gas mixture can be derived from a gas ideal-solution. At the same time, this example also highlights how the pressure and the composition influence the ideal character of a mixture.
