TME20403

INTRODUCTION TO THERMODYNAMIC ENGINEERING

LAB REPORT 4
The Study of Phase Change

LECTURER: SAFAA NAJAH SAUD AL-HUMAIRI

NO STUDENTS NAME MATRIX NO. COURSE

1 Nur Hidayah Binti Abu Bakar Sidik 012020091935 BETE

2 Goh Wen Han 012021021062 BETE

3 Mohamed Umair Ali 012020020409 BME

4 Sharan Dev A/L Ramesh 012021021619 BME

Objective
- To study the phase change of a substance from liquid to solid by plotting the cooling curve.
- To determine the melting point of the given substance and to find out the transition time.

Theory
The term change of phase means the same thing as the term change of state. The change of phase always occurs with
a change of heat. However, the temperature does not change. When we heat a solid, the energy supplied is used to
increase the kinetic energy of its molecules, and thereby its temperature increases. Energy is required to melt a solid,
because the cohesive forces between molecules must be partially overcome to allow the molecules to move about.
Similarly, energy is required to vaporize a liquid, because in so doing the molecules are separated and molecular
attractive forces are overcome. But there is no temperature change until a phase change is complete. i.e., during phase
change, the energy supplied is used only to separate the molecules ; no part of it is used to increase the kinetic energy
of the molecules. So, its temperature will not rise since kinetic energy of molecules remains the same.

The process, phase transition is governed by Newton's law of cooling, which states that,
" The rate of change of temperature of an object is proportional to the difference between its own temperature and the
temperature of its surroundings."

i.e., ,

where, T is the temperature of the

object k is a positive constant
Tais the temperature of the surroundings.

By studying the phase change of a substance from solid to liquid, one can determine the melting point, latent heat of fusion
etc of the substance.

In order to understand more about the theory of phase change, consider a sample cooling curve for a substance with
a melting point of 450 C.
The flat portion of the graph represents the phase change from liquid to solid at the constant melting temperature 45 0 C.
The two curved portions represent cooling of the liquid plus the tube (left) and cooling of the solid plus the tube (right).
These cool according to Newton’s law of cooling,
where T is the temperature of the sample, T0
is room temperature, and k is a positive
constant.

The heat loss rate of the liquid plus the

boiling tube is likely to be the same as the
heat loss rate of the solid plus the tube for a
given temperature difference (T-T0)

The specific heat C2 of the material undergoing phase change is, however, unlikely to be the same for the liquid
and the solid phases.
Thus, we have

and

where upon it can be seen that the cooling constants in the liquid (l) and solid (s) phases are related by the

equation
These cooling constants can be estimated by using the graph to estimate the time te taken for the
material plus the tube to cool to 1/e of their starting temperature above room temperature. Then since
the solution to the Newton’s law of cooling differential equation is

we have k = 1/ te.
The heat loss rate of the liquid plus the boiling tube is likely to be the same as the heat loss rate
of the solid plus the tube for a given temperature difference (T-T ) 0
Materials

• Naphthalene
• Ice
• Wax

Procedure

- Procedure for doing the Simulator:

a. The desired sample has been selected from the combo box Select Substance.
b. The mass of the substance has been varied by using the slider Mass of the Substance.
c. By using the slider Surrounding Temperature, the temperature of the surrounding
has been selected.
d. The mass, radius and thickness of the boiling tube has been varied by using the
sliders given under the heading Boiling Tube.
e. The experiment has been started by clicking on the Start the Experiment button.
f. Then the sample in the boiling tube has begun to melt.
g. The temperature of the sample has been noted from the digital thermometer given
in the simulator.
h. Also, time has been noted from the stopwatch given in the simulator.
i. The time-temperature observation has also been plotted there.
j. The melting point and the transition time of the sample has been obtained by
clicking an option Show Result.

- Procedure for doing Real Lab:

a. The mass material 1 of the empty boiling tube is taken.

b. Sample of mass material 2 is put into the boiling tube. It is melted by keeping the
test tube immersed in hot oil bath. The sample melts into clear liquid.
c. When it is melted completely, the test tube is taken out, wiped dry, suspend in air,
and allowed to cool.
d. A thermometer is immersed into the melt. A stopwatch is started and the
temperature is noted for every equal interval of time. The time temperature
observation is taken till the liquid get frozen into solid and gets cooled to room
temperature.
e. Draw a cooling curve by taking time along the X axis and temperature along Y-axis.
The temperature corresponding to the horizontal region will give the transition
temperature.
f. The time for the transition time is also noted from the graph. The experiment is
repeated for different samples.
Results and Calculations

Surrounding
Materials Mass if Temperature Transition Time Melting Point
Substance (g) (℃) (min) (℃)
Naphthalene 10 28 0.1258 80.26
Ice 10 28 0.5905 0
Wax 10 28 0.1316 45
1. Find the transition time of 20g naphthalene with the surrounding temperature as 30 ℃. Let the
boiling tube has mass 25g, diameter 2.5cm and thickness 0.15cm.

2. How much time does 30g of ice takes to melt at a surrounding temperature of -5℃? (We are using
a boiling tube having mass = 20g, radius = 1.5cm, thickness = 0.2cm)
3. In the above experiment, let the surrounding temperature is changed to 0℃. What will be the chan
ge in the transition time for ice?

4. Repeat the experiment for different surrounding temperatures and study the variation of melting
point of ice.
5. Calculate the melting point of wax having a mass 30g. Let we are using a boiling tube of mass25g
, having a thickness 0.5 cm and radius 1.5 cm. (Choose surrounding temperature as 40℃.)
Results

The table below shows the materials specifications and the control factor in the experiment
conducted today

Material Naphthalene Ice Wax Glass

Weight 10g 10g 10g -
Surrounding 28 28 28 -
temperature
Specific heat 1.72 J.g-1K-1 4184 J⋅kg−1⋅K−1 2200 J/g K. 840 J/g K
capacity

Table below represents the simulation for each material under the conditions stated above for 60s,
with each reading taken 3 seconds apart

Naphthalene
Time Temperature
0 218
1 162
2 122
3 97
4 79
5 62
6 52
7 45
8 40
9 36
10 34
11 32
12 31
13 30
14 29.6
15 29.4
16 29.195
17 28.83
18 28.6
19 28.44
20 28.21
21 28.15
22 28.11
23 28
24 28
 Ice
Time Temperature
0 100
1 78
2 62.635
3 52.75
4 44.66
5 40.05
6 36.25
7 33.79
8 31.97
9 30.75
10 29.911
11 29.39
12 28.91
13 28.66
14 28.46
15 28.32
16 28.223
17 28.153
18 28.107
19 28.07
20 28.05
21 28.037
22 28.025
23 28.01
24 28.0125
25 28.0086
26 28
27 28
28 28
29 28
30 28
 Wax
Time Temperature
0 218
1 181
2 150
3 125
4 104
5 90.43
6 77.75
7 67
8 60
9 53.64
10 48
11 44
12 40.7
13 38.54
14 36.30
15 34.57
16 33.41
17 32.28
18 31.27
19 30.68
20 30.215
21 29.752
22 29.368
23 29.104
24 28.87
25 28.691
26 28.54
27 28.39
28 28.30
29 28
30 28
Graphs and observation

The data from the tables above are graphically represented below

NAPATHELENE
250

200
TEMPERATURE

150

100

50

0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
TIME

ICE
120

100

80
TEMPERATURE

60

40

20

0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
TIME
 WAX
250

200
TEMPERATURE

150

100

50

0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
TIME

From the results obtained from phase change diagrams, the transition time and melting point of the
samples were obtained the values for each material is represented below

Material Naphthalene Ice Wax

Transition Time/ min 0.1258 0.5905 0.1316
Melting point /Celsius 80.26 0 45

Discussion

There are three basic states of matter, solid, liquid and gas. The goal of this experiment was to determine
the energy involved in the phase changes of Naphthalene, Ice and wax. The energy changes were
observed by recording the temperature of the sample up until room temperature and by reading the
graphs. The energy of phase change experiment uses the concept of heat fusion which is the changing
of phase when freezing or milling. From the results we’ve obtained through out the experiment we can
observe Ice had the highest transition time compared to the other 2 with 0.5905mins for the transition
take place, while naphthalene and wax had a transition time of 0.1258minutes and 0.1316 minutes
Conclusion
To conclude our experiment on phase change, when a substance transitions from one phase to another,
its temperature remains constant. The difference between a substance's own temperature and the
temperature of its surroundings determines its rate of temperature change. There is no change in
temperature until the phase transition is complete. The energy supplied is only required to separate the
molecules; none of it is used to increase the molecule’s kinetic energy. Therefore, the temperature will
not rise since the kinetic energy of the molecule remain constant. To summarize, phase change is
isothermal.
Reference

The Study of Phase Change.

Bibliography:

1. Carey, Van. Liquid Vapor Phase Change Phenomena. Washington: Taylor &
Francis, 2007.
2. Abell, Martha and James Braselton. Introductory Differential Equations, Third
Edition. Boston: Academic Press, 2009.
3. Avison, John. The World of Physics. Cheltenham: Nelson Thornes Ltd, 1989.
4. Schröder, Bernd. A Workbook for Differential Equations. New York: Wiley, 2009.

Webliography:

1. en.wikipedia.org/wiki/Cooling_curve
2. www.ugrad.math.ubc.ca/coursedoc/math100/notes/diffeqs/cool.html
3. en.wikipedia.org/wiki/Paraffin