1. The document describes an experiment to investigate the cooling curve of candle wax by heating it until melted and then measuring its temperature every 30 seconds as it cooled. 2. The melting point of candle wax was determined to be 53.5°C as the temperature remained constant for 3 minutes during the solidification process. 3. According to the kinetic theory, particles in solids vibrate in place while liquid particles can move freely, explaining why brown flakes in the wax remained still after solidification.

1. RonaldoDegazon Wednesday09/05/12 Physics:Lab#8 Thermal Physics
Aim: To investigate the coolingcurve of asubstance.
Apparatus: candle wax,testtube,testtube holder,Bunsenburner,tripod&beaker,thermometer,
stop-clock,retortstand, water& wire gauze,glassrod
Diagram:

2. Procedure:
1. The apparatus wasset upas shownin DiagramA, withthe substance ina water
bath.
2. The substance washeateduntil itwascompletelymeltedandwell above itsmelting
point.
3. The test tube containingthe substance wasremovedandplacedinaretortstand,
withthe thermometerinthe liquidasshowninDiagramB.
4. The stop-clockwasstartedand the temperature wasrecordedeveryhalf minute
until itfell towell below itsmeltingpoint.The thermometerwasnotremoved
duringsolidification.
5. The substance wasre heatedtoa temperature above itsmeltingpointsothe
thermometercouldhave beenremovedfromthe substance.
6. A coolingcurve of F versust wasplottedforthe substance.
Results:
Time / s Temperature / o
C
30 62
60 59.5
90 57
120 56.5
150 55
180 54.5
210 54.5
240 54
270 54
300 53.5
330 53.5
360 53.5
390 53.5
420 53.5
450 53.5
480 53.5
510 53
540 52.5
570 52.5
600 51
630 51
Time / s Temperature / o
C
660 50.5
690 50
720 50
750 49.5
780 49
810 48.5
840 48
870 47.5
900 47

3. Discussion:
The meltingpointof a substance is the temperature at which it changes from a solid to
liquid. Also the process in which a liquid turns into a solid is called solidification which occurs at the
freezingpoint;the exactopposite of the melting point. When a substance solidifies, the heat released
during that process is called the latent heat of solidification.
From the experiment, it was deduced that the melting point of candle wax was 53.5 o
C
because itremainedatthat temperature for 180 seconds.Heatwas being lostduringthatperiod butthe
temperature did not fall at all. Therefore it was concluded that the heat was no lost but was used to
repair the bonds of the molecules. The heat used during that 180 seconds is its latent heat of
solidification.
Dark brown flakes were noticed moving around in the candle wax when melted.
However,whensolidified,these flakesremainedstill.Thiscanbe accountedforwiththe Kinetic Theory.
The theorystatesthat liquidsconsistof clustersof particlesthatare free tomove and that solids consist
of fixedparticleswhichare restricted from moving but only vibrate about a fixed point. When the wax
was melted,the brownflakesmovedaroundfrombeingbombardedbythe movingclustersinthe liquid
wax.However,whenthe wax solidifiedthere wasnomovementamongstthe particlesand so the flakes
no longer moved.
The KineticTheory can alsobe usedto explainthe shape of the graph.First it states that
all matter is made of tiny particles. It goes on to say that these particles when supplied with energy,
move fasterandhence theiraverage kineticenergyincreases.Average kinetic energy is proportional to
temperature, hence the more heat supplied the higher the temperature. Applying the theory to this
experiment,youcouldsaythatthe more heat releasedbythe candle wax, the lower its average kinetic
energy fell and hence the lower its temperature dropped.
From points A to B, as more heat was released by the candle wax, the lower its
temperature fell hence the downwards trend in the line. However, from B to C the line remained
straight– the wax’stemperature remainedconstant. Thisissimplybecausethe beinglostwasnot being
absorbedbythe wax’ssurroundings,itwasbeingusedto repair the bonds of the molecules, hence the
average kineticenergyof the particlesdidnotfall.Nevertheless,whenthe bondswere repaired and the
wax had solidified,the surroundingsresumedabsorbingthe heatfromthe wax,hence from C to D there
is another downward trend.
Sources of Error:
- Human ReactionTime:there wasa possibilitythat the temperature reading was not
taken exactly 30 seconds after the previous reading.
- Parallax Error: there was a possibility of a parallax error when reading the scale of
the thermometer.

4. - There wasthe possibilitythatthe wax wouldhave meltedtooquicklyandvaporized.
- There wasa possibilitythat the thermometer would take the reading of the tube’s
temperature and not the wax’s.
Precautions:
- To reduce parallax error, the thermometer reading was taken with the eye
perpendicular to the level of liquid in the thermometer.
- The test tube containing the candle wax was heated indirectly in a water bath to
control the rate at which it was heated so that it didn’t melt too quickly.
- It was ensured that the thermometer did not touch the bottom of the test tube to
ensure that the temperature of the wax was taken and not the tube.
- A glass rod was used to stir the water to ensure that its temperature remained
uniform throughout.
Conclusion: A cooling curve was successfully obtained for candle wax.