Chapter 12

Q. 12.5.2

Answer the following questions based on the phase diagram (not drawn to scale) for ammonia, NH_{3}.
a. What is the normal melting point? The normal boiling point?
b. At what temperature and pressure do the three phases coexist in equilibrium?
c. Is ammonia a solid, a liquid, or a gas at room temperature and pressure? If a gas, is it a permanent gas?
d. Which is the more dense phase, the liquid or the solid?



Verified Solution

You are asked to answer questions about the physical properties and physical state of a compound.
You are given the phase diagram for the compound.
a. Normal refers to a pressure of 1 atm. The point on the liquid–solid line with a pressure of 1 atm has a temperature of 195.4 K. This is the normal melting point. The point on the liquid– vapor curve with a pressure of 1 atm occurs at a temperature of 239.8 K. This is the normal boiling point.
b. Look for the one point that all three phases have in common (T). This is the triple point at 195.3 K and 0.059 atm.
c. Take room temperature and pressure to be 298 K and 1 atm. This corresponds to the point indicated by the letter X on the diagram, which is in the gaseous region. Ammonia is a gas at room temperature, but it is not a permanent gas. Because the temperature is below the critical temperature (405.5 K), it can be liquefied by increasing the pressure to about 11 atm at 298 K.
d. The liquid–solid equilibrium line has a positive slope. Therefore, the solid is more dense than the liquid.