Week 6 IMF

Question 1

What type of process is vaporization and condensation? Are they physical changes/chemical changes?

Answer 1

Vaporization is endo
Condensation is exothermic (they are backwards)
Physical changes!

Question 2

FOR WATER: At 25 C Hvap=44Kj/mol, At 100 C Hvap=40.8. Why are these values different at different temp

Is this the same for most liquids?

Answer 2

At 100 C, one mol of water already has more thermal energy than one mol of 25 C THEREFORE less thermal energy in needed to be gained to vaporize 1 mol of liquid

No, generally BP smaller at 25 C

Question 3

What is dynamic equilibrium?
Vapor pressure?
What is the external pressure for a pot of water?
Boiling pt

Answer 3

Dynamic equilibrium- rate of vap=rate of condensation
Vapor pressure- gas pressure at dynamic equlibrium with its liquid
Atmospheric pressure
Boiling pt: temperature at which the vapor pressure is equal to atmospheric pressure

Question 4

What are the observations between:
1. vapor pressure and Temperature
2. boiling point and Pressure

Answer 4

1. Vapor pressure increases with temperature because higher T, higher thermal energy and more molecules with sufficient kinetic energy escape the liquid surface
2. Boiling point increases with pressure because stronger forces hold the molecules down

Question 5

Supercritical fluids
What is the interface/ what happens to the interface as temperature increases

Answer 5

Exist at a specific critical pressure and above the critical temperature (exhibit both liquid and gas properties)
- The interface is what seperates the gas and liquid phases . As temperature increases, it becomes non existant

Question 6

Sublimation
Deposition
Which is endo/exothermic

Answer 6

Sublimation: Overcome IMF to produce a change of state from solid to gas (endo)
Deposition: The process of change of states from gas to solid (exo)

Question 7

Fusion and heat of fusion & Freezing

Endo/exothermic?

Answer 7

Fusion/melting: Overcoming IMF to produce change of state from solid to liquid (endo)
heat of fusion: Heat required to melt one mold of solid to liquid
Freezing: The process of change of state from liquid to solid (exo)

Question 8

What is an obervation between heat of fusion and heat of vaporization

Answer 8

Heat of fusion are significantly less than heats of vaporization because there are more IMF interactions to overcome

Question 9

What are the 3 exothermic processes
What are the 3 endothermic

Answer 9

1. Exo: Condensation (G to L), Freezing (L to S), deposition (G to S)
2. Endo: Fusion (S to L), Vaporization (L to G), Sublimation (S to G)

Question 10

What is the heat of vaporization and heat of fusion for water

Answer 10

HVap=40.7 kJ/mol
Hfus:6.02 kJ/mol

Question 11

What does downward slope in a phase diagram represent

Answer 11

Donwards slope is atypical which indicated liquid has higher density than solid

Question 12

What are the unique properties of water (5)

Answer 12

• Solid is less dense than liquid
• Strongest IMf in solid (ice)
• 4 Hydrogen bonds per water molecule (open structure)
• Liquid at room temp despite its small molar mass
• Water has high heat capacity