In what region of the phase diagram would a substance certainly be a liquid? #a)# Past the triple point temperature #b)# Any spot past the melting point #c)# Between the melting point and critical temperature #d)# Between the melting and boiling points
The best answer choice is
Consider a general phase diagram:
The liquid phase has two degrees of freedom: we can change temperature or change pressure, and we still remain with a liquid.
Anything at reasonably high pressure (between
- It is not enough to be past the triple point temperature, because being left of the solid green curve gives you a solid. Therefore, it is NOT
- "Any" is immediately a sign that
#(b)#is false. Clearly, if we are past the melting point, we could very well be past the boiling point, and thus we could have a gas, not a liquid.
- Being between the melting point and critical temperature is almost correct... but it is easy to do that while still having too low a pressure, thus giving a gas.
#(c)#is NOT a good answer but is on the right track...
- Being between the melting and boiling temperature is OK at the appropriate pressures (between
#P_(tp)#and #P_(cr)#is a guarantee). #(d)#is the most accurate answer out of all of them, but it is still not a complete enough answer.