[timchai]

i want to ask how can CO2 maintain at solid to liquid , how u descrpe the condition , i don't understand why in HKAL , he said only pressure higher than triple pt (i don't rember)

[ARGOS++]

Dear timchai;

Which phases are required for your statement and how are they related to the Triplepoint in the diagram:

http://www.standnes.no/chemix/english/phase-diagram-co2.htm

Good Luck!
                    ARGOS⁺⁺

[cliverlong]

i want to ask how can CO2 maintain at solid to liquid , how u descrpe the condition , i don't understand why in HKAL , he said only pressure higher than triple pt (i don't rember)

When I input the title of your post into Google I get the following two entries in first and second position. The information is there

http://www.science.uwaterloo.ca/~cchieh/cact/c123/phasesdgm.html
http://en.wikipedia.org/wiki/Carbon_dioxide

What do you know about phase diagrams?
Look at the labels on the axes: pressure vertically and temperature horizontally. Look at the areas that are labelled solid, liquid, gas. Do you understand the diagram?

Clive

[timchai]

Am i correct, for solid turn to gas
the solid should lie below pressure 5.11 atm and temp . -56.4 and then start to increase temp. or either decrease pressure
am i correct

[ARGOS++]

Dear timchai;

You are correct!, - If you mean not to pass the liquid phase!

Do you know how the line is called that divides solid from gas phase?

Do you know  how the other lines are called? Otherwise see on:

http://en.wikipedia.org/wiki/Phase_diagram

Good Luck!
                    ARGOS⁺⁺

[azmanam]

on CO₂ phase diagram:

http://www.chemistry-blog.com/2009/02/04/chemistry-lab-demonstrations-liquid-co2-extraction/

[timchai]

thx