11 particulate model (changes in state & temp curves)
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Interactive Science Volume A
Chapter 11
Part (e)
Thermal Physics
HEATING CURVE The heating curve, as the name implies, plots out the entire graph of the changes
in the states of matter as temperature increases over time. Such a plot helps us identify fixed temperature points like the melting and boiling
points of the substance. This also allows us to identify which state the substance would be in at a given temperature or a given time.
Temperature /oC
Time /min
Boiling point
Melting point
Solid state
Solid & Liquid state
Liquid state
Liquid & gaseous state
Gaseous state
Part (e)
Learning to interpret a heating/cooling curve will help you identify a certain state the substance will be in easily and quickly for a given temperature or given time.
52
Thermal Physics
Temperature / oC
Time / min
0
100
Solid State
Melting:
Solid & Liquid States
Melting begins
Melting ends
Liquid state
Boiling:
Liquid & Gas StatesBoiling begins
Boiling ends
Gas
Consider the heating curve for pure water:
Part (e)
53
Thermal Physics
HEATING CURVE
Temperature /oC
Time /min
Boiling point
Melting point
Solid state
Liquid state
Gaseous state
Part (e)
-Constant temperature-Breaking of inter-molecular bonds-Energy Absorbed-Phase Change
54
Thermal Physics
COOLING CURVE The cooling curve, on the other hand, plots out the entire graph of the changes in
the states of matter as temperature decreases over time. Once we understand how a heating curve works, interpreting such a curve is like
working backwards.
Part (e)
The heating curve displays the temperature behaviour of a substance when it is gaining energy, while the cooling curve displays what happens to the state when the substance loses energy.
Temperature /oC
Time /min
Condensation point
Freezing point
Solid state
Solid & Liquid state
Liquid state
Liquid & gaseous state
Gaseous state
55
Thermal Physics
Temperature / oC
Time / min
0
100
Solid
Melting:
Solid & Liquid States
Freezing beginsFreezing ends
Liquid
Condensing:
Liquid & Gas States
Condensation begins
Condensation ends
Gas
Consider the cooling curve for pure water:
Part (e)
56
Thermal Physics
COOLING CURVE
Part (e)
Temperature /oC
Time /min
Condensation point
Freezing point
Solid state
Liquid state
Gaseous state-Constant temperature-Formation of inter-molecular bonds-Energy Released-Phase Change
57
Thermal Physics
Let’s Review
Thermal Physics
1. The picture below shows the cooling curve for alcohol. At which temperature is alcohol likely to boil?
A) Above 78 oC B) At 78 oC C) At - 15 oC D) Below - 15 oC
Review Exercise (Heating & Cooling Curves)
10
Temperature /oC
Time /min
78
- 15
Solid
Liquid
Gas
Thermal Physics
2. The diagram shows part of the heating curve for substance U. What is the point X known to be?
A) Melting point B) Boiling point C) Room temperature D) Temperature axis
Review Exercise (Heating & Cooling Curves)
11
Temperature /oC
Time /min
X
Solid
Liquid
Thermal Physics
3. The diagram shows part of the heating curve for Iron. What is the state of Iron at point B?
A) Liquid B) Solid C) Liquid & Solid D) Gas & Liquid
Review Exercise (Heating & Cooling Curves)
12
Temperature /oC
Time /min
Melting point
A
B
C
Thermal Physics
4. Which of the following correctly describes the states of the substance at points 1 to 2 and 4 to 5?
Review Exercise (Heating & Cooling Curves)
13
Temperature /oC
Time /min
1
2 3
4 5
6
a) From 1 – 2, the substance changes from gas to liquid. From 4 - 5, the substance freezes to become solid.
b) From 1 – 2, the substance is at gaseous state. From 4 - 5, the substance is at liquid state.
c) From 1 – 2, the substance starts changing into liquid. From 4 - 5, the substance remains at liquid state.
d) From 1 – 2, the substance is at gaseous state. From 4 - 5, the substance freezes to become solid.
Thermal Physics
5. Which of the following correctly describes what takes place at temperature Y?
Review Exercise (Heating & Cooling Curves)
14
Temperature /oC
Time /min
Y
Liquid
Gas
a) The particles in the substance lose energy, but moves more vigorously within a fixed, regular arrangement.
b) The particles in the substance overcome intermolecular forces and move at high speeds. Temperature continues to increase.
c) The particles in the substance overcome intermolecular forces and move at high speeds. Temperature remains constant.
d) The particles in the substance gain energy and slide past one another, forming new bonds. Temperature remains constant.
Thermal Physics
6. Which of the following correctly describes what happens to the substance at points 2 to 3 and 5 to 6?
Review Exercise (Heating & Cooling Curves)
15
Temperature /oC
Time /min
1
2 3
4 5
6
a) From 2 – 3, the substance changes from liquid to gas. From 5 - 6, the whole substance has been converted to gas.
b) From 2 – 3, the substance melts, bonds are broken and solid changes to liquid. From 5 – 6, the substance boils, bonds are broken and liquid changes to gas.
c) From 2 – 3, the substance melts, bonds are broken and solid changes to liquid. From 5 – 6, the substance completes boiling and everything has been converted to gas.
d) From 2 – 3, freezing takes place and the substance changes from liquid to solid. From 5 – 6, the substance completes boiling and everything has been converted to gas.
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