91Ó°ÊÓ

Suppose you cool a mixture of 50% nitrogen and 50% oxygen until it liquefies.

The term "liquefying" refers to the transformation of a liquid from another state, such as a gaseous to a liquid or a solid to a liquid.

Temperature graph for the mixture is:

Consider the experimental phase diagram for nitrogen and oxygen at atmospheric pressure in Figure 5.31 of the book. If we take a horizontal line from the upper curve to the lower curve (until they intersect), we can see that the x = 0.75 from the lower curve, and since pure nitrogen occurs at x = 0, we can conclude that the mixture is in a gaseous state as we lower the temperature.

The liquefying process will continue as we lower the temperature; follow the bottom curve until it hits x = 0.50; there must be no gas left at this point; drawing a horizontal line, we can see that the temperature at this point is 81.6 K.