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. We're going to compare positive or endothermic cube solution and negative or exothermicial solution. We're also going to compare non ideal situations we're presented to by dashed lines and ideal situations they're presented by solid lines. Now, in this graph, the y axis is vapor pressure and the x axis is the mole fraction.