Heat of Vaporization of a Liquid
Purpose:
In this laboratory activity you will determine the relative volatility and the heats of vaporization
of water, ethanol, and acetone.
Background Information:
Acetone, ethyl alcohol, and water are three liquids that have different physical and chemical
properties. Differences in physical and chemical properties of these particular solvents make
each useful for particular purposes. One of these properties is volatility. A volatile liquid is one
which evaporates quickly. Variation in volatility is one of several physical and chemical
properties which separate one liquid from another.
The table below lists other characteristics which distinguish one substance from another.
Molecular Mass Freezing Point
g/mol
o
C
Boiling Point
o
Heat of Vaporization
C
cal/gram
Water
18
0
100
540
Ethanol
46
-114
80
204.3
Acetone
58
-94
57
134.7
The freezing point of a substance can be related to another property called the heat of fusion. The
heat of fusion is the amount of heat necessary to change one gram of solid to one gram of liquid
at the freezing point. Boiling point is a physical property which can be related to the substance’s
heat of vaporization. The heat of vaporization is the amount of heat necessary to change one
gram of liquid into one gram of vapor at the boiling point of the liquid.
The lower the heat of vaporization, the lower the boiling point of the liquid. As a consequence of
a lower boiling point, the lower the heat of vaporization, the more volatile the liquid.
Equipment:
Digital thermometer
Graduated cylinders, 100 mL
Stopwatches
Chemical and Consumables:
Acetone
Distilled water
Ethanol
Procedure:
1. Obtain a graduated cylinder containing one of the three liquids to be tested.
2. Place the digital thermometer into the cylinder and leave it in the liquid at least 30 seconds.
Note and record the temperature of the liquid.
3. Take the thermometer out of the liquid and observe the temperature at all times. The partner
should begin timing the process. Hold the thermometer vertically and record the highest
temperature.
4. Continue observing the temperature as the thermometer cools until the temperature begins to
level. Stop timing and record the lowest temperature observed.
5. Rinse off the thermometer with water and carefully dry it with a paper towel.
6. Repeat the above procedure with each of the other two liquids.