It is important to develop mathematical relationships for predicting the behavior of fluids/gases under any imaginable condition of pressure, temperature and volume (P-V-T). This is a very challenging problem. The way science approaches these sorts of problems is to introduce simplifications of the physical reality, by formulating a set of assumptions and coming up with a base model that might be called ideal. From that point on, once the base model has been established, one looks at a real case by estimating how close (or far) it performs, with respect to the base (ideal) case, and introducing the corresponding corrections. Such corrections will take into account all the considerations that the original assumptions left out.