2. Objectives
At the end of the lesson, students should be able to:
define melting and freezing.
define boiling and condensation
interpret the heating curve
3. Internal energy
The internal energy of a body is the combination
of the total kinetic energy (due to molecular
motion) and potential energy (due to inter-
molecular forces) of the molecules in the body.
An increase in temperature leads to an increase
in the kinetic component of the internal energy.
When the temperature
increases, the molecule
move faster
4.
5. Melting and Freezing
Melting is a process in which a substance
changes its state from solid to liquid..
Solid Liquid
The temperature at which this happens is called
the melting point of the substance.
6. Melting and Freezing
Freezing is a process in which a substance
changes its state from liquid to solid.
Solid Liquid
The temperature at which this happens is
called the freezing point of the
substance.
Melting point = Freezing point
7.
8. Boiling and Condensation
Boiling is the process in which a substance
changes from the liquid state to the gaseous
state.
Liquid Gas
The temperature at which this happens is called
the boiling point of the substance.
9. Boiling and Condensation
Condensation is a process in which a substance
changes from the gaseous state to the liquid
state.
The temperature at which this happens is called
the condensation point of the substance.
Boiling point = Condensation point
10. State of matter
gaseous
state
boiling point
liquid
state
melting point
solid
state
11. Change of State
solid liquid gas
melting / boiling /
freezing point condensation point
12. Take note!
During the change of state
(freezing/melting/boiling/condensation), the
temperature of the substance remains constant.
For example, when pure ice is melting at 0 °C,
it will remain at 0 °C until all the ice has melted.
The temperature of pure water will increase
beyond 0 °C, when more thermal energy is added to
the water.
13. Heating curve
Temperature / °C
This is a Temperature time
graph.
In this example, water is being
heated from -10 °C
As you can see, the
temperature of water rises to
-10 °C.
0
Time / s
-10 ice Heat supplied →
14. Heating curve
Temperature / °C
When the temperature of water
reaches 0 °C, the ice melts.
During the change in state, there is no
change in temperature even though
thermal energy is still being
transferred to the water.
ice → liquid
0
(melting) Time / s
-10 ice Heat supplied →
15. Heating curve
Temperature / °C
100
After all the ice has
melted, water will
liquid
continue to increase in
Change in state, no temperature
change in temperature
ice → liquid
0
(melting) Time / s
-10 ice Heat supplied →
16. Heating curve
Temperature /
°C
Change in state, no
change in temperature
liquid → steam
100
(boiling)
liquid
Change in state, no
change in temperature
ice → liquid
0
(melting) Time / s
-10 ice Heat supplied →
17. Heating curve
Temperature / °C
120 Change in state, no
change in temperature
steam
liquid → steam
100
(boiling)
liquid
Change in state, no
change in temperature
ice → liquid
0
(melting) Time / s
-10 ice Heat supplied →
18. Cooling curve
120 °C
steam
steam → liquid
100 °C
(condensation)
liquid
0 °C liquid → ice
(freezing)
ice
-10 °C
Heat removed →
