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Phase Changes
Phase Change
It is a transition between solid, liquid, and gaseous phases typically involve large amounts of energy compared to the specific heat.
Latent Heat
Is the HEAT released or absorbed by a body during a change of state without change of temperature.
Energy is absorbed from the air to melt solid ice into liquid water without any change is temperature.
Energy is also absorbed to change water into steam without any change in temperature.
Heat of Fusion
Heat of Vaporization
Melting
Freezing
evaporation
condensation
Phase Change Diagram
Simple Recall
The change from solid to liquid is.
The change from liquid to solid.
Melting
Freezing
Simple Recall
The change from gas to liquid
The change from liquid to gas
Condensation
Vaporization
Simple Recall
The change from solid to gas.
The change from gas to solid.
Sublimation
Deposition
Heat of Phase Change
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.
Calorimetry
..Or the state of measurement of exchanging quantities of heat
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
Problem Solving
Given : m = 30g , m = 85g at 25 C ,T =5 C
Find : m
A glass weighing 30g contains 85g of water at 25o C. How much ice at 0 C will be needed to bring the temperature down to 5 C? The specific heat of glass is 0.16cal/g, and that of water is 1.00 cal/g.
O
water
O
glass mix
ice
O O
Problem Solving
Solution:Let H (heat absorbed by ice) ---
(m )(80cal/g) H (heat absorbed by melted ice) ---
(m )(1.00cal/g C )(25 C – 5 C) H (heat given off by glass) ---
(30 g)(0.16cal/g C )(25 C – 5 C) H (heat given off by water) ---
1
ice
2
ice.O
O O
3 . O O
4