Transcript Slide 1

Heat &Heating Curves
The change in the internal energy of a
substance causes the change of phase.
Energy Absorbed
SOLID
LIQUID
Energy Released
GAS
Energy enters your hand from a
hot stove because ___________
the stove is
warmer than your hand
__________________________.
If you touch ice, energy passes
hand into _________.
the ice
from your
________
Heat (in joules)(J):
energy transferred due to a
temperature difference
(always from higher to lower)
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
&
• PE stored in
solid attractions
(IMAFs)
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)
Heating Curve
same temp during
phase change
(=KEavg)
What happens
to added heat?
melt
vaporize
added heat
breaks IMAFs
& increases
distance (↑PE)
Heating Curve of Water
endothermic
(↑KE)
gas
exothermic
Temp (oC)
100oC
0oC
boiling
condensation
boiling point
(↑PE)
(↑PE)
liquid
(↑KE)
melting
freezing
solid
(↑KE)
Time (of Heat Added)
Temp (oC)
100oC
0oC
Heating Curve of Water
Why is ∆Hvap >>> ∆Hfus?
heat of
LG takes more
vaporization gas
(2260 J)
energy to break
(∆Hvap)
IMAFs than SL
•heat required
liquid to vaporize
(or condense)
heat of
fusion
(334 J)
(∆Hfus)
•heat
required
solid
to melt (or freeze)
Time (of Heat Added)
Cooling Curve of Water
gas
Temp (oC)
100oC
condensation
boiling
The phase change
sequence is reversible.
liquid
freezing
melting
0oC
solid
Time (of Heat Added)
Quick Quiz!
1. Temperature is directly proportional to the
_________ of a substance.
A. thermal energy
B. vibrational kinetic energy
C. average kinetic energy
D. total kinetic energy
Quick Quiz.
2. Heat is simply another word for _________.
A. temperature
B. internal energy
C. energy transferred from hot to cold
D. thermal energy
Quick Quiz.
3. Molecules with stronger IMAFs will have…
A. higher heats of vaporization
B. higher heats of fusion
C. higher boiling points
D. higher melting points
E. higher viscosity
F. higher specific heat capacity
G.higher surface tension
H. ALL of the above