Hi

Q656)
This is a trick question. You are correct that that all three phases will co-exist in equilibrium at the triple point. But don't forget that this represents the phase diagram for water, so at 0 degrees C and 1 atm, we should remember that ice and liquid water will coexist (phase change). All solids and liquids will always have equilibrium with their vapour pressure, so therefore making C the correct answer.

Recall that pools still lose their water (slowly) even below 100 degrees C. This is due to the exchange between the surface of the liquid water and the atmospheric pressure. (vapour pressure!)

Q708)
Answers A and B are the same, and hence incorrect (and possibly a typo). The main thing to notice about this questions is that it indicates "after the salt has dissolved". Therefore, hydrostatic pressure is the pressure exerted by a liquid AT REST.

Recall that this is more of a Physics type question, as "hydrostatic pressure" is listed as a physics topic, and not a Chemistry topic.

Q713)
You have to determine whether you are creating more order or more disorder in the system. Therefore, you are dealing with entropy. This particular concept is popular on the MCAT. As one goes from a pure liquid to a solution (salt dissolved in liquid), one is creating more disorder. The Na+/Cl- are spread throughout the liquid, and disrupts the order, and also pushes the water molecules further apart from one another. Since pure water is zero, this means increasing the disorder (negative delta S), will result in a negative osmotic pressure (as defined in the text).

Hope this helps!

Chad Maheux