Name:_________________________________Period_____Date__________________________
Chemistry Liquids and Solids Check Off Review Answers
boiling point
condensation point
critical point
critical pressure
critical temperature
dipole-dipole force
dispersion force
gas
liquid
solid
hydrogen bonding
intermolecular force
London force
phase diagram
melting point
freezing point
sublimation
deposition
supercritical fluid
triple point
vapor pressure
volatility
Use your notes and other resources to answer the following questions:
1. Discuss the Physical conversion of states of matter.
solids Melt liq evaporate gases
Gas  Condense liq  freeze  solid
Solid  Sublimate  gas; gas  deposition  solid
2. Discuss hydrogen bonding, dipole-dipole, and London Dispersion Forces
o Hydrogen bonding is a special case of dipole-dipole. Only occurs when Hydrogen is bonded to N, O, or F.
o Molecules that Hydrogen bond also have dipole-dipole and London forces
o London forces depend upon particle size and particle shape. Larger the particle and the larger the shape the
greater the London forces. In the end, London forces come down to the number of electrons (i.e. MM).
o All substances have London forces involved. Non-polar molecules have only London forces
3. Define dynamic equilibrium
Dynamic Equilibrium- Two opposing processes that occur simultaneously at equal rates
4. Name three ways to increase the rate of evaporation.
 Increasing the temperature increases the kinetic energy of the molecules in the liquid. Because they have
more energy, more molecules are likely to make the transition from the liquid phase to the gas phase.
 Lowering the pressure also increases the rate of evaporation. If you lower the external pressure, the vapor
pressure necessary for evaporating - and thus the temperature necessary for evaporating - drops.
 Increasing surface area also increases evaporation, because with a larger surface area, more molecules have
a chance to make it into the vapor phase.
5. a. Why does evaporation cause cooling?
The temperature of the water is determined by the average of the speed of all the molecules. When water
evaporates at room temperature, some fast-moving, highly energetic molecules have enough energy to overcome
the attractions that individual molecules have for one another and enter the gas phase. As these high-energy
molecules leave the liquid phase, the molecules still in a liquid state are the slower ones (their average energy is
lowered). Thus the temperature of the remaining water is lower. That’s why evaporation causes cooling.
5. b. Will the remaining liquid evaporate as fast as the initial liquid?
When the particles with the highest kinetic energy leave the substance, the average kinetic energy of the remaining
particles decreases. The temperature of the substance therefore decreases. Lowering the temperature of a liquid
decreases the rate of evaporation.
6. Define Vapor Pressure.
The vapor pressure of a liquid is the equilibrium pressure of a vapor above its liquid (or solid); that is, the pressure of
the vapor resulting from evaporation of a liquid above a sample of the liquid in a closed container.
7. What does the strength of vapor pressure depend on?
 If the intermolecular force is strong, the fraction of molecules that have enough energy to escape into the
vapor is small and the vapor pressure will be small.
 Increasing the temperature increases the average kinetic energy of the liquid molecules, and hence the
fraction of molecules with sufficient energy to escape from the liquid phase increases with temperature.
8. Why do liquids with low intermolecular attractive forces have high vapor pressures?
If the intermolecular force is relatively weak, a large fraction of the molecules have enough energy to be able to
escape into the vapor which results in a large vapor pressure.
9. At 20°C, the vapor pressure of substance X is 700. mmHg and that of substance K is 33 mmHg.
a. Which substance has the higher vapor pressure?
Substance X
b. Which substance will have the lower normal boiling point?
Substance K
c. Which substance has the stronger intermolecular forces?
Substance K
10. Determine which of the following molecules has the lowest VP. The molecules are CO2, CH4 and PCl3.
Remember to use all your resources to determine what kind of molecules you have. (Draw them to be sure)
O=C=O
H
│
H—C—H
│
H
Cl
│
Cl—P—Cl
11. a. Define Boiling Point in terms of vapor pressure
Boiling Point- Temperature at which the vapor pressure of a liquid is equal to or above the external pressure.
b. Factors affecting the Boiling Point of a substance:
Increasing the external pressure increases the Boiling Point. Decreasing the pressure decreases the Boiling Point
c. Factors affecting Boiling Point differences between substances:
1. Molecular size & Molecular mass
2. Attractive forces between molecules
12. Explain how and when does a substance boil?
Water starts to vaporize long before it boils. So liquid water turning into water vapor happens anyway.
As the water heats up you will see lots of little bubbles forming in the water.
But when there are so many bubbles that they can easily escape (e.g. the vapor pressure equals the atmospheric
pressure), they proceed to escape, so that the vapor pressure remains the same as the atmospheric pressure.
13. At 760 mmHg & 100°C, large bubbles begin to form within a sample of water. What is contained in the bubbles?
Water Vapor is contained in the bubbles.
14. Describe at least two differences between the processes of evaporation and boiling.
 Evaporation happens at any temperature above melting point, boiling only at the boiling point.
 Evaporation happens only at the surface, boiling happens throughout the liquid.
 Boiling takes energy in (endothermic) to occur, while evaporation lets only the molecules with the highest
kinetic energy out, leaving the rest of the water cooler, so evaporation is exothermic.
15. Why is the boiling point for water different in the mountains then at normal sea level?
The boiling point is lower because the air is thinner, and there is less pressure acting on the water. This means that
you have to add less energy to counteract the forces holding the water in liquid form. This would translate it into a
longer time to cook something in the water as compared to cooking the same object at sea level.
16. The vapor pressure of a substance at 25°C is 835 mmHg. If the atmospheric pressure is 758 mmHg, will the
substance be a liquid or a gas at 25°C?
The substance will be a gas.
17. Define Critical Temperature and Critical Pressure of a liquid.
 The critical temperature of a substance is the temperature at and above which vapor of the substance
cannot be liquefied, no matter how much pressure is applied.
 The critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature.
18. Discuss Phase Diagrams and identify the Phase Change boundaries. (see VP Curves & Phase Diagrams)
Point out the triple point, the critical temperature and pressure coordinates, supercritical fluid, normal
boiling point, normal melting point, positive slope of S/L equilibrium line, negative slope of S/L equilibrium
line, L/G equilibrium line, S/G equilibrium line