# Hydrogen phase transition

A sample of hydrogen at a pressure of 7.10×10-2 atm and a temperature of 26.4 K is compressed at constant temperature to a pressure of 18.5

Which of the following are true? 1. One or more phase changes will occur 2. The sample is initially a solid. 3. The liquid initially present will vaporize. 4. The final state of the substance is a liquid

The sample is initially a gas

MY ANSWER: I feel that one or more phases will change and that the liquid present will vaporize as it surpasses the supercritical point.

• – Mithoron Sep 27 '15 at 18:02
• How is this any different from your previous question? – Ben Norris Sep 27 '15 at 18:04
• I accidentally double posted it after putting my answer in the body. Im fixing that now. – Chastity Sep 27 '15 at 18:06
• Say, do you think you could screenshot the phase diagram and upload it? It'll make it much easier to see. You can crop out the question since it's already been typed out. – orthocresol Sep 28 '15 at 5:37
• Regarding the question itself, 1) you already said that the sample is initially a gas - so the "liquid initially present" can't be vapourised if there's no liquid initially present. 2) a note on terminology: the point on the phase diagram is called the critical point, and the substance is called a supercritical fluid. 3) A supercritical fluid only forms when both $T$ and $p$ exceed that of the critical point. Check the diagram on Wikipedia: en.wikipedia.org/wiki/… – orthocresol Sep 28 '15 at 5:42