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.