Download phase diagrams and IMF

Name: _________________________________________
Date:____________________________
Homework 4- OPTIONAL ONLY – not for credit
1.) Explain why the formation of solid and/or liquid phase(s) would be favored under conditions of:
Explain using the ideas of kinetic energy (molecular motion), how close together molecules
are/could be, ability to be attracted to its neighbor:
a. high pressures
b. low temperatures
2.) Will the boiling point of water be higher or lower than 100oC on top of Mt. Everest? Explain
why/how you made your choice.
3.) Therefore what effect does increasing the atmospheric pressure have on the boiling point of a
liquid – explain your choice?
4.) Use the phase diagram for water (above). It is not drawn to scale. The triple point occurs at
0.0060 atm and 0.01oC. Using this knowledge, answer the following questions:
a. Label the triple point – use this as a reference point for the following questions (put a dot
there!)
b. The vapor pressure of liquid water at 90oC is 0.69 atm locate this point on the phase
diagram and label it
c. What is the most stable state of water at 90oC and 0.5 atm?
d. What will happen if the pressure is increased from 0.006 atm to 1.5 atm while the
temperature remains at 90oC?
5.) Distinguish the differences between intermolecular forces and intramolecular forces. Which type
of force is stronger? Would you expect a bond dissociating to take more energy than the energy
needed to vaporize a sample? EXPLAIN
6.) Would you expect to find a significant degree of H bonding between a pure sample of: If a
molecule exhibits H-bonding, please draw an example of this
a. NH3? Explain.
b. CH3OH? Explain.
c. HBr? Explain.
7.) You have two containers. One contains only dimethyl ether, the other only contains ethanol.
Which substance would you expect to have the higher vapor pressure (put more molecules into the
gas phase), dimethyl ether or ethanol? EXPLAIN citing the types of IMFs that each sample has.
8.) Explain why the boiling point of pure liquid NaCl would be higher than NaCl dissolved in water
(HINT: think about the type of IMFs there would be for each sample!!!)
9.) Which of the following would have the greatest polarizability – briefly explain your choices (one
explanation is good for all if done correctly!)?
a. N or F
b. Al+3 or Na+1
c. Cl or I
d. P-3 or S-2
THINK about the types of IMFs each sample would have and then answer the question!
10.)
The boiling point of phosphine (PH3) is -88oC while the boiling point of ammonia (NH3) is
-33oC. Thus, the boiling point of phosphine is LOWER than that of ammonia even though PH3
has twice the molar mass. Why?
11.)
Which substance in each pair would you expect to have the higher boiling point?
EXPLAIN your choice:
a. H-F or H-Br
b. CH3CH2OH or HO-CH2CH2-OH
12.)
Phosphine (PH3) and hydrogen sulfide (H2S) each contain 18 electrons. What is the molar
mass of each? The dipole moment of PH3 is 0.58 D and the dipole moment of H2S is 0.97D.
Which would have the higher boiling point? Boiling is a “derivation” of vaporization, so which
would have the greater heat of vaporization (Hvap)? (boiling is when all the molecules in a
sample turn to the gas phase (based on vapor pressure and atmospheric pressure) while
vaporization is when the molecules on the surface of a liquid turn into the gas phase)