Experiment
2
HEAT OF VAPORIZATION OF
LIQUID NITROGEN
Purpose
Nitrogen is the major (78% by mole or by volume) component of air. Even
though N2 is a gas at room temperature (N2 boils at 77 K [-196oC]), it is possible
to obtain it in the liquid state. In this experiment the energy needed to boil one
gram of liquid nitrogen will be determined by letting a known mass of it
interact with warm water in a Styrofoam cup (a calorimeter). The boiling
nitrogen will cool the water. The energy given up by the water will be used to
vaporize the nitrogen; this is the heat of vaporization, ΔHvap.
Liquid Nitrogen Safety
Liquid nitrogen is cold enough to cause severe frostbite upon contact with
living tissue. Wear proper safety gear when handling liquid nitrogen to prevent
contact with the liquid or inhalation of extremely cold vapor. Make sure
exposed skin surfaces are covered. Safety splash goggles must be worn.
Do not enclose liquid nitrogen in a sealed container. It boils so rapidly that the
phase transition from liquid to gas can generate a lot of pressure which can
result in bursting or explosion.
Experimental Procedure
In this experimental procedure, it is assumed that vaporization of the liquid
nitrogen uses energy provided by the warm water. The water is prepared in an
insulated container and then liquid nitrogen is added to the water.
1. Heat about 100 mL of water in a 250 mL beaker to about 70oC.
2. Determine and record the mass of a Styrofoam cup (call this cup #1) to the
nearest 0.1 g.
Portions of this laboratory are adapted from materials furnished by Lee Marek - Marek@aol.com,
lmarek2@uic.edu , lmarek@fnal.gov; WEB: http://www2.chem.uic.edu/marek/
3. Add the hot water to the cup and determine the total mass.
Styrofoam cup in a 600 mL beaker to stabilize the setup.
Set the
4. Determine the mass of another empty Styrofoam cup to the nearest 0.1 g.
Add about 60 g of liquid nitrogen to the cup. Record the mass of the cup and
nitrogen you took to the nearest 0.1 g. The nitrogen will steadily boil to vapor,
so go directly to your lab station while your lab partner is doing step 5.
5. While the liquid nitrogen is being "massed", determine the temperature of
Record the value as the initial
the warm water to the nearest 0.1oC.
temperature right before you add the nitrogen. The temperature will be lower
than 70oC; do not worry just use whatever temperature you are at.
6. Remove the thermometer and immediately add the liquid nitrogen to the
cup with the hot water. Wait for the boiling to stop. Do not put the
thermometer back in until the "sizzling" has stopped. You may have to fan the
fog away with your hand. If any ice has formed make sure it has melted before
measuring the final temperature. You may have to tilt your cup to let the water
melt the ice.
7. Record the temperature of the cooled water as soon as the liquid nitrogen
has fully evaporated and any ice has melted.
8. Determine the final mass of the Styrofoam cup and cool water.
Observations –
include in the in lab portion of your notebook
Data Analysis
1. Calculate the change in temperature of the water.
2. Calculate the energy (in the form of heat) released (lost) by the water in
joules using the average mass of the warm and cold water and the specific heat
of water, cs in an equation that relates heat transfer to a temperature change:
heat lost by the water = mH2O cs(H2O) ΔT
3. How much energy did the liquid nitrogen gain in boiling? (Consider the law
of conservation of energy.)
4. Calculate the heat of vaporization of nitrogen in J g-1 N2.
5. What would be the heat of condensation of nitrogen in J g-1 N2?
6. Using the results of this experiment, determine the number of joules
required to vaporize one mole of nitrogen, N2. This is called its molar heat of
vaporization, ΔHvap.
7. Write a chemical equation to represent each of the following processes for
N2 and include the energy term in J mol-1 N2 in the equation. State whether the
process is exothermic or endothermic.
a) Vaporization:
b) Condensation:
8. What errors were inherent in this experiment and the equipment you used?
How could you reduce these errors? Explain how these errors would affect your
results (high, low, or no effect).
9. What kind of energy (potential or kinetic) was involved in the phase change?
Explain (in terms of energy transfer) what occurred in this experiment.
10. What do you think the identity of the fog was that was produced when the
liquid nitrogen was added to the water?
11. Calculate the volume of N2 gas at STP produced in the vaporization of your
liquid nitrogen sample.
Conclusions –
include in the post lab
Additional Questions to Answer in Your Report
1. The following results were obtained in an experiment on an unknown (liquid
Y). Calculate the heat of vaporization of the unknown liquid in units of J g-1.
mass of liquid Y
average mass of water
initial temperature of water
final temperature of water
specific heat of water
42.6 g
96.1 g
55.0oC
44.5oC
4.18 J g-1 oC-1
2. On a molecular level what is happening to the liquid nitrogen? Describe this
and use a drawing to show the changes being described.
Liquid

Gas
3. Look up the value for the heat of vaporization of liquid nitrogen in the
Handbook of Chemistry and Physics or the NIST website. Calculate the % error
in your experiment.
4. Which possesses more kinetic energy at its boiling point, N2 liquid or N2 gas?
Explain.
5. The heat of fusion of nitrogen is 25.7 J g-1 N2. Why is the heat of fusion
lower than the heat of vaporization?
A Sample Data Table
DATA
MASS 0F STYROFOAM CUP #1
____________
MASS OF STYROFOAM CUP #1 + HOT WATER
____________
MASS OF LIQUID NITROGEN
_____________
INITIAL TEMPERATURE OF HOT WATER
____________
FINAL TEMPERATURE OF WATER
_____________
MASS OF STYROFOAM CUP #1 + COOL WATER
_____________
RESULTS
MASS OF HOT WATER
_____________
MASS OF COOL WATER
_____________
AVERAGE MASS OF WATER
_____________
CHANGE IN TEMPERATURE
_____________