So at any given time, less molecules will be able to escape in a non ideal fluid than in an ideal fluid. And because there are less molecules present in the states above the pressure will be less. Therefore, the stronger the intermolecular forces, the less likely that they will evaporate. Likewise, the weaker the intermolecular forces holding the molecules together, the more likely that they will evaporate. Now, let's look at some graphs for non ideal fluids. Now in this graph we're going to compare two situations.