Answer to Question #172794 in General Chemistry for andyndnt

Question

Visualize a substance with the following points on the phase diagram: a triple point at 0.10 atm and 55 K; a normal melting point at 68 K; a normal boiling point at 183 K; and a critical point at 50 atm and 218 K. The solid liquid line is “normal” (meaning positive sloping). For this, complete the following:

1. Roughly sketch the phase diagram, using units of atmosphere and Kelvin. Label the area 1, 2, and 3, and points T and C on the diagram.

2. Describe what one would see at pressures and temperatures above 50 atm and 218 K.

3. Describe the phase changes from 25 K to 100 K at 25 atm.

4. What exists in a system that is at 1 atm and 183 K?

5. What could be the necessary condition for this substance to sublime?

Answer 1

3) A pressure of 50 kPa and a temperature of 50 °C correspond to the “water” region—here, water exists only as a liquid. Notice that the liquid-vapor curve terminates at a temperature of 374 °C and a pressure of 218 atm, indicating that water cannot exist as a liquid above this temperature, regardless of the pressure.

4) Oxygen exist in its all state at 1 atm and 150 K because it is its critical point. Critical point is the temperature at which any matter exist in its all physical state at same temperature.

5) Sodium Chloride is an ionic solid and has high melting and boiling points. So it can not change in vapour phase simply at atmospheric pressure hence it cannot sublime.
Ammonium chloride, dry ice and iodine undergo sublimation which on heating without coming in the liquid state directly convert in a gaseous state.