1. Phase Changes

2. Phase Change
 It is a transition between solid, liquid, and gaseous
phases typically involve large amounts of energy
compared to the specific heat.

3. Latent Heat
 Is the HEAT released or absorbed by a body during a
change of state without change of temperature.
Heat of Fusion
Energy is absorbed from the air to melt solid ice into
liquid water without any change is temperature.
Heat of Vaporization
Energy is also absorbed to change water into steam
without any change in temperature.

4. Phase Change
Diagram condensation
evaporation
Freezing
Melting

5. Simple Recall
The change from solid to liquid is. Melting
The change from liquid to solid. Freezing

6. Simple Recall
The change from gas to liquid Condensation
The change from liquid to gas Vaporization

7. Simple Recall
The change from solid to gas.
Sublimation
The change from gas to solid.
Deposition

8. Heat of Phase Change
Calorimetry
 Nature demands that energy always be conserved:
The heat lost by objects of decreasing temperature
must be equal to the heat gained by objects of
increasing temperature.
..Or the state of measurement
of exchanging quantities of
heat

9. Here, if heat is added to a body, then the value is
positive; and if the heat is taken from a body, then the
value is negative. Since energy (in this case heat) is
always conserved, then:
 Heat added (+) + Heat taken (-) = 0
 Heat added = heat taken

10. Problem Solving
 A glass weighing 30g contains 85g of water at 25o C.
How much ice at 0 O C will be needed to bring the
temperature down to 5 O C? The specific heat of glass is
0.16cal/g, and that of water is 1.00 cal/g.
O O
 Given : m glass= 30g , m water = 85g at 25 C ,T mix =5 C
 Find : m ice

11. Problem Solving
 Solution:
Let H (heat absorbed by ice) ---
1
(m )(80cal/g)
ice
H 2 (heat absorbed by melted ice) ---
(m ice )(1.00cal/g .OC )(25 OC – 5O C)
H 3 (heat given off by glass) ---
(30 g)(0.16cal/g . C )(25O C – 5O C)
H 4 (heat given off by water) ---