Experimental measurement of heat of vaporization 11

Experimental measurement of heat of vaporization 11

※ Note

1. Invited the students did not wear glasses, wear goggles to carry out the experiment.

2. Liquid nitrogen is very, very cold, never let the liquid nitrogen or liquid nitrogen cooling-off objects to touch the body or clothing.

3. Pour a cup of liquid nitrogen in the heat, about seven points over, and the lid must not be covered.

4. Do not drop anything into the liquid nitrogen.

5. The aluminum block when placed in liquid nitrogen slowly so as to avoid the rapid boiling of liquid nitrogen, a short rope that is established for this purpose.

【Objective】

Measurement unit mass of liquid nitrogen heat of vaporization.

【Instruments】

Liquid nitrogen, thermal insulation glass, aluminum block, code table, electronic scales.

【Methods】

Atmospheric pressure in an aluminum heat C (T) with temperature as shown in Figure 1, the area under the curve, indicating the temperature of aluminum rose to T2 from T1, the unit mass of the required heat. If the aluminum block (mass m) from room temperature (T2) to reach a thermal equilibrium with the liquid nitrogen (T1) the period (), reduction in the quality of liquid nitrogen, then the liquid nitrogen heat of vaporization per unit mass of

‥ ‥ ‥ ‥ ‥ ‥ ‥ ‥ ‥ ‥ ‥ ‥ (1)



【Step】

1. Observation of the background measured vaporization rate of liquid nitrogen will be fitted  liquid nitrogen flask with aluminum block placed on electronic scales, the records of quality changes every 10 seconds, recording 10 data, calculate the average background of vaporization rate of liquid nitrogen.

2. The aluminum block tied with cotton thread and placed in liquid nitrogen, the need to slowly add in order to avoid a sudden overflow of liquid nitrogen, and so completely into the aluminum block completely, the use of electronic records in liquid nitrogen mass balance changes in circumstances over time . This section required to record data once every 5 seconds, record time, about 3 minutes, by the data determine the time about the first few seconds, aluminum block and nitrogen balance.

3. In determining the liquid nitrogen balance with aluminum block, the need to record the background after the experiment vaporization rate, record data once every 10 seconds, recording 10 data have been obtained after the experiment in liquid nitrogen evaporation rate of the background.

4. By (1), calculated per unit mass of liquid nitrogen heat of vaporization.

5. Repeat steps 1 to 3 for at least five times its average demand and the average standard deviation. And draw the liquid nitrogen Mass Change and Time Chart.



【Problem】

In the method requested the use of data or a graphic shows you how to determine the aluminum block to reach thermal equilibrium with the liquid nitrogen at the time.