← All Labs
Lab 10

Heat of Vaporization of Liquid Nitrogen

Unit 1⏱ 90 minGuided Inquiry

Overview

How can we determine the heat energy needed to vaporize a liquid?

Objectives

  • How can we determine the heat energy needed to vaporize a liquid?
  • Connect observations to AP Chemistry models and calculations.
⚠️ Wear protective goggles and an apron. Follow your teacher’s safety directions for all chemicals and equipment.

Materials Needed

Procedure

1

Prepare a data table like the one provided by your teacher. Record all masses to the nearest 0.01 g unless otherwise noted.

2

Heat about 100. mL of water in a 250 mL beaker to about 50 - 60 degrees Celsius .

3

Determine the mass of a Styrofoam cup (#1).

4

Add the hot water to the cup and determine the total mass. Place the Styrofoam cup in a large (600 mL) beaker for stability. ***Do Steps 4 and 5 simultaneously***

5

Tare a second empty Styrofoam cup. Your teacher will add about 80 mL of liquid nitrogen to the cup. Determine the mass of the nitrogen and the cup, then allow enough nitrogen to evaporate until a 60.00 g sample of nitrogen remains. (Remember to take into account the mass of the cup - you want a 60.00 g sample of nitrogen).

6

Determine temperature of the water to the nearest 0.l oC , then remove the thermometer.

7

Quickly and carefully add the liquid nitrogen to the warm water. Observe. When the boiling stops, or when you no longer hear a "sizzling" sound, fan away any remaining fog and swirl the water gently to melt any ice that may have formed. Do not reinsert the thermometer until these processes are finished.

8

Record the final temperature of the water.

9

Determine the final mass of the cup and cool water.

Pre-Lab Questions

1. What was your result for your experimental Heat of Vaporization? What was your % error? Identify at least two sources of error in this lab that would affect your heat of vaporization value. Would these errors cause a higher or a lower value for your Heat of Vaporization result? How could these errors be reduced? What was the composition of the fog produced when the liquid nitrogen was added to the hot water? How does the1st Law of Thermodynamics (Conservation of Energy) apply to this lab? Why did the water lose mass after the liquid nitrogen was added? Explain

Post-Lab Questions

1. The heat of fusion of N2 (s) is 25.7 J/g. Why is this value so much lower than that for the heat of vaporization of N2 (l)?