Experiment 10

HEAT OF VAPORIZATION OF LIQUID NITROGEN

ANALYSIS

1.  You will graph all three sets of data for the three intervals using the spreadsheet and use a straight line fit to the data to determine the mass loss rate during each interval. Follow the procedure below for all three intervals. Steps 2 and 3 pertain to Interval #1, but you should repeat them for the other two intervals as well.

2.  Use the mouse to select the mass vs. time data for Interval #1 in cells A15:B36.

3.  Now that the plot is set up, you will perform a linear (straight-line) fit to the data in order to determine the slope:

4.  Take the average of the rates for the first and last 10 minute intervals in cells F29 and F88, and record the value in cell F97. Subtract this average from the rate for the middle interval in cell F60 to find the boil-off rate due to the measured power input from the heater. Record this value in cell F99.

5.  From the voltage and current data in cells F39:F40, calculate the power using equation (1). Record the value in cell F41 as indicated.

6.  Divide the power in cell F41 by the boil-off rate calculated in cell F99, and record the result in cell F100. The resultant value is the heat of vaporization in joules/g. Convert this value to joules/kg and place the answer in cell F101.

7.  As displayed in cell F102, the accepted value of the heat of vaporization of nitrogen is 1.992 x 105 joules/kg. How does this compare with the heat of vaporization you measured? Find the percentage error between your results and the accepted value, and enter in cell F103.

8.  Print out your Worksheet and complete your lab report.