Materials Science

Introduction

The molar enthalpy of vaporization of liquid hexane was determined by the process of evaporating all hexane out of the evaporator, and measuring the temperature drop of the surrounding.

Theory

The vaporization of a liquid hexane is endothermic. The temperature is measured in toluene, which has a low heat capacity and has a very good thermal conductivity. Molar enthalpy of vaporization of hexane can be calculated from the following equation:

∆H vap.m = Eit/m ((θA-θB)⁄(θC-θD)).

Experimental procedure

The voltage was set or adjusted to give a current of exactly 1A, and the apparatus was set as shown in figure 1, of the lab manual. By doing a test on the battery it was made certain that the voltage reading was just above or below 1V and the range had four decimal places. Finally the thermistor was read for every 30 seconds for about 5 minutes, then water pump was turned on for the rest of the experiment, then hexane was evaporated and still the temperature was read, lastly the power supply was switched on and temperature was also read for some few minutes.

Results

The data obtained in the experiment are listed below in table 1 and are plotted in figure 1.

Table 1: Thermistor reading due to time for vaporization of hexane.

Time/sec Temp/⁰C

0.5 1.1764

1 1.1739

1.5 1.1712

2 1.1687

2.5 1.1662

3 1.1639

3.5 1.1616

4 1.1596

4.5 1.1577

5 1.1558

5.5 1.151

6 1.1476

6.5 1.1444

7 1.1411

7.5 1.1379

8 1.1348

8.5 1.1319

9 1.1292

9.5 1.1268

10 1.1255

10.5 1.1246

11 1.1231

11.5 1.1217

12 1.1247

12.5 1.141

13 1.1537

13.5 1.1633

14 1.1715

14.5 1.1796

...