Question

Using the phase diagram for `CO_2`, what phase is carbon dioxide in at -60`"^@`C and 15 atm pressure?

Answer 1

Well, consult the phase diagram.

And then you literally just read it like any other graph: find your `x` coordinate and find your `y` coordinate.

`(x,y) -= (P,T) = ("15 atm", -60^@ "C")`

And one should easily see that `"CO"_2` is a solid at this `T` and `P`, as it should be, left of its triple point temperature but higher up than the triple point pressure.

We call this dry ice; once obtained and brought into a laboratory, it spontaneously sublimes.