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If I am given a phase diagram, how can I determine which phase will have more density?

What should I consider to solve these kinds of questions?

Does the answer have to do with the area that each phase occupies? Or the more area a phase occupies, the more the density?

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The solid phase is more dense than the liquid phase. The line that separates solid and liquids bends right.

If the solid phase is less dense than the liquid phase, the line that separates solid and liquids bends left.

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    $\begingroup$ Welcome to chemistry.stackexchange.com. Feel free to take a tour of the site. $\endgroup$
    – Jan
    Feb 12 '16 at 1:28
  • $\begingroup$ This could really do with some explanation of the Clapeyron equation, it is technically an answer, but not much of one $\endgroup$
    – orthocresol
    Feb 12 '16 at 18:59
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Look at the lines on the phase diagram. If you go to a line and then increase pressure you move to a new phase, the denser phase. Edit: Add the below.

enter image description here

Go to the dotted green line. Now, go straight up (increase in P). What happened? You went from solid and liquid being in equilibrium to just liqui. The liquid is more dense than the solid.

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  • $\begingroup$ could you be more clear ! $\endgroup$
    – Maher
    Aug 13 '14 at 14:46
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The phase which has the higher density is the phase which exists under higher pressure and lower temperature. Thus, in a phase diagram showing pressure as a function of temperature, look for the phase which lies in the upper left region.

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Usually the solid phase is the densest. To be sure, look at the slope of the solid-liquid line. If it is decreasing, the liquid phase is denser, if it is increasing, the solid phase is denser. For example, the phase diagram of water has a negative solid-liquid line; the liquid phase of water is denser.

The densest phase exists at the highest pressure and lowest temperature. This comes back to looking at the top left corner of the graph.

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