1. Heat &Heating Curves
The change in the internal energy of a substance causes the change of phase.
Energy Absorbed
SOLID
LIQUID
GAS
Energy Released

2. (always from higher to lower)
Energy enters your hand from a hot stove because ___________
__________________________.
If you touch ice, energy passes from ________ into _________.
Heat (in joules)(J):
energy transferred due to a temperature difference
the stove is warmer than your hand
your hand
the ice
(always from higher to lower)

3. (translational motion) (vibrational & rotational motion)
Internal Energy:
total of all KE + PE
(translational motion)
gas
KE of moving molecules
KE of moving atoms in molecules
(vibrational & rotational motion)
Internal
Energy
liquid
&
solid
Demo – raise and drop textbook loudly (twice)
PE stored in attractions
(IMAFs)

4. The distance between particles.
Ice melts by absorbing heat, but without increasing temperature.
0oC solid  0oC liquid
(avg KE stays same)
What changes?
The distance between particles.
(PE increases)

5. added heat breaks IMAFs & increases distance (↑PE)
Heating Curve
same temp during phase change
(=KEavg)
What happens to added heat?
vaporize
added heat breaks IMAFs & increases distance (↑PE)
VLC – media file (Changes of State)
melt

6. Heating Curve of Water (↑KE) gas (↑PE) liquid (↑KE) (↑PE) solid (↑KE)
endothermic
(↑KE)
gas
exothermic
boiling
100oC
boiling point
condensation
(↑PE)
liquid
Temp (oC)
(↑KE)
(↑PE)
melting
0oC
freezing
solid
(↑KE)
Time (of Heat Added)

7. Heating Curve of Water heat of vaporization heat of fusion
Why is ∆Hvap >>> ∆Hfus?
heat of vaporization
LG takes more energy to break IMAFs than SL
gas
(2260 J)
100oC
(∆Hvap)
heat required to vaporize (or condense)
liquid
Temp (oC)
heat of fusion
(334 J)
0oC
(∆Hfus)
heat required to melt (or freeze)
solid
Time (of Heat Added)

8. The phase change sequence is reversible.
Cooling Curve of Water
gas
condensation
100oC
boiling
liquid
The phase change sequence is reversible.
Temp (oC)
freezing
0oC
melting
solid
Time (of Heat Added)

9. Quick Quiz!
Temperature is directly proportional to the _________ of a substance.
thermal energy
vibrational kinetic energy
average kinetic energy
total kinetic energy

10. Quick Quiz.
Heat is simply another word for _________.
temperature
internal energy
energy transferred from hot to cold
thermal energy

11. Quick Quiz.
3. Molecules with stronger IMAFs will have…
higher heats of vaporization
higher heats of fusion
higher boiling points
higher melting points
higher viscosity
higher specific heat capacity
higher surface tension
ALL of the above