PASCO TD-8557A Basic Calorimetry Set - Manual (Page 11)

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B a s i c C a l o r i m e t r y S e t
9
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 arrange-
ment 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
).
IMPORTANT: Always remove the steam tube from the water before turning off the steam generator
heat. (Can you explain why?)
Tubing -
25 cm
Tubing -
35 cm
Water
Trap
Steam
Generator
Glass tube
to restrict
opening
Figure 3.1