Must be a total of 300 words; 150 for each discussion question.
Discussion 1—Carbon dioxide phase diagram
The phase diagram for carbon dioxide is available here
http://en.wikipedia.org/wiki/Supercritical_carbon_dioxide
Discussion 2—Water phase diagram
The phase diagram for water can be described here.
http://www.earth.northwestern.edu/people/seth/202/new_2004/classnote_figs/h20phase.jpg
On explanation for the how ice skates work is that a thin film of liquid water is formed at the interface between the skate blade and the ice, creating a lubricating layer.