PASCO TD-8557 Basic Calorimetry Set - Manual (Page 10)

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B a s i c C a l o r i m e t r y S e t
8
Experiment 3: Latent Heat of Vaporization
Equipment Needed
• Calorimeter
• Thermometer
• Steam Generator
• Water Trap
• Tubing
• Balance
If a steam generator is not available, a distillation flask and
Bunsen burner is adequate. A second flask can be used as a
water trap.
Introduction
When a substance changes phase, the arrangement of
its molecules changes. If the new arrangement has a
higher internal energy, the substance must absorb heat
in order to make the phase transition. Conversely, if
the new arrangement has a lower internal energy, heat
will be released as the transition occurs.
In this experiment you will determine how much
more energy is contained in one gram of steam at
100°C, than in one gram of water at the same temperature. This value is called the Latent
Heat of Vaporization of water.
CAUTION: This experiment involves the use of boiling water and steam. Work carefully.
Procedure
1. Measure T
rm
, the room temperature.
2. Set up a steam generator with a water trap as shown in Figure 3.1. The tube lengths
should be approximately as shown in the figure.
3. Determine M
cal
, the mass of a the empty, dry calorimeter.
4. Fill the calorimeter approximately 1/2 full of cool water about 10° C below room
temperature.
5. Turn on the steam generator and wait for the steam to flow freely for at least a minute.
6. Measure T
initial
and M
cal + water
, the temperature of the cool water and the mass of the
water plus calorimeter.
7. Immediately immerse the free end of the short tube into the cool water in the calorim-
eter. Stir the water continuously with the thermometer.
IMPORTANT: The bottom of the water trap should be kept higher than the water level in the calorime-
ter to avoid water being pulled from the calorimeter back into the water trap.
8. When the water temperature, T, gets as far above room temperature as it was initially
below room temperature, remove the steam tube. Continue stirring the water and
record the highest stable temperature attained by the water (T
final
).
CALORIMETER
MAX TEMP: 100 °C
P/N: 650-02975
Figure 3.1: Equipment set-up
tubing, 25 cm tubing, 35 cm
glass tube to
restrict opening
water
trap
steam
generator