Few quantities cause so much trouble with units as does pressure, In a typical general chemistry course, the student encounters pressure measured in atmospheres, pascals, Ton, and pounds per square inch. The conversion factors among all these units are apparently arbitrary and follow no sensible pattern. In addition the gas constant, R, appears with quite different numerical values when it is expressed using each of those pressure units. (Thankfully, the version of R using pounds per square inch is rarely used.) R also occurs in general chemistry in energy units, as 8.314 J/(mol K)j In my experience, students find the various numerical values of R mysterious, can see no connection between the energy and pressure-volume versions, and usually must resort to simple unit analysis to decide which particular value of R is needed in a given problem.
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