Heat of Vaporization of Nitrogen Peter Hamlet Plttsburg State University, Pittsburg, KS 66762
This simple measurement takes a class less than 30 min and can be integrated into existing calorimetry experiments as an introduction to the nrocess. The violent boiling and billows of fog that result w6en liquid nitrogen is poureionto water nrovide a memorable e x a m ~ l eof a Dhase chanee. and there h e no complicating factors in the &u~ation'td distract attention from the concept that enerm -- used to vanorize nitrogen is lost by the ~ a t e ; . The presence of liquid nitrogen also provides an opportunity to observe its dramatic hehavior.I.2 The author will supply instructions for students upon request. Experlmenial Heat 100 g of water to about 55 OC, and put it in an 8-oz styrofoam cup. Weigh about 60 gof liquid nitrogen into another 8 m styrofoam cup. Do not touch liquid nitrogen because extended contact will damage skin. Measure the temperature of the hot water. Remove the thermometer, and dump all the liquid nitrogen onto the hot water. Wait until the sound of boiling stops. Fan away the fog by hand. Take the new temperature of the water. If all heat lost by water is used to boil nitrogen, the following equation will get the heat of vaporization of nitrogen:
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Journal of Chemical Education
heat of vaporization of nitrogen = 14.184 Jg-' of waterNwater temperature change) . - 'C-'Nmass . .. (mass of liquid nitrogen)
Students enter their data and calculated heat into the lab computer, which corrects calculation errors and compares each student's results to the handbook value of 199.1 Jg-I oC-1.3 The results of 202 student measurements show 150 values clustered between 174 and 213. The remaining values are widely scattered and are not included in the statistics helow. The distribution resembles a square wave with a top that rises from left to rieht. The averaee is 195. The average deviation from the hanihook value is 4%.A more complicGed ex~erimentthat evanorates the nitrogen with electric heat does not get any better results.4
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Alyea, H. N.; Dutton, F. B., Eds. TestedDernonstrations in Cham i s m J. Chem. Educ.: Easton. PA, 1965: p 220. Bailey. P. S.; Bailey. C. A,: Andersen, J.; Koski, P. G.; Rech. stainer, C. J. Chem. Educ. 1975, 52, 524. Dean. J. A,. Ed. Lange's Handbook of Chemistry, l2ih ed.; McGraw-Hill: New York. 1979; p 9-120. Knutton, P. A.: Salinger, G. L. Phys. Teach. 1969, 7, 288.
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