ON THE TEACHING OF THE DIFFERENT FORMULATIONS OF THE VIRIAL EQUATION

Chemistry educators teaching chapters on "real gases" usually present to the students the "virial development" of Kamerlingh Onnes for the equation of state, which takes into account interactions of the molecules in aggregates by a successive series of parameters (B, C, etc.), yielding a polynomial equation on the concentration (equivalent to the inverse of the molar volume). A well known transformation of the virial equation to a polynomial equation as a function of pressure is also widely used, with suitable coefficients (B', C', etc.). The literature presents relationships between the second and third virial coefficients for both equations, for example B' = B/RT. Students usually assume that both formulations should deliver to similar calculated results. However, when using the relationships mentioned above to perform calculations for the same gas conditions of pressure and temperature, discrepancies are observed in the molar volume obtained by the two formulations of the virial equation. Chemistry educators are required to present such discrepancies, explain them and interpret them. In addition to that, a possible alternative practical approach is to develop a relationship between the second virial co