Measuring Specific Latent Heat of Vaporization ofWater
Introduction:
The aim of this experiment was to determine the specificlatent heat of vaporization of a liquid using basic equipment and calculations.The accepted value of the latent vaporization heat is 2.3x 104 Jkg-1.Hopefully the results obtained will be similar to the accepted value.
Apparatus:
Kettle
3 beam Scales
Stop watch
Variables:
Method:
1. Take the kettle and fill it up half waywith water
2. Put it on the scales and measure themass
3. Record the mass in the data table
4. Turn on the kettle
5. When the water starts to boil starttiming
6. Stop timing when 50 grams of water havebeen lost
7. Record in the data table
8. Repeat steps 1-7 five times
Data Collection and Analysis
Time of the trialsTrials Mass/kg ± 0.005 Time/s ± 5s 1 0.050 187 2 0.050 180.0 3 0.050 180.0 4 0.050 192 5 0.050 145 Average 0.050 186
Uncertainties
The scientist determined the uncertainties bymeasuring them. The scientist wasn’t sure when to start timing the boilingwater, and as there was no set time time written in the procedure, so theuncertainty was determined to be 5s. As the scales used to measure the mass of thewater were not electronic, but three beam, the minimum uncertainty was determinedto be 5 grams. The uncertainty for the specific latent heat of vaporizationwas based on the uncertainties of mass and time.
Pt=mLv />
Trial 1 m=0.05 t=187s
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Trial 2 m=0.05 t=180s
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Trial 3 m=0.05g t=180s
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Trial4 m=0.05kg t=192s
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Trial 5 m=0.05kg t=189s
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AverageTrials 1 2 3 4 5
Lv /Jkg-1
2.7 x 106
±349110
2.6 x 106
±338688
2.8 x 106
±355622
2.6 x 106
±338688
2.1 x 106
±237300
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Conclusions and evaluations
The calculated value of the specific latent heat ofvaporization was supposed to be 2.3 x 106 J/Kg. Unfortunately theresults achieved by the calculations were not perfect and did not reach theaccepted values. All the Lv calculated were in one range, but didnot come close to 2.3 x 106.
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The median value of the calculated Latent heat ofvaporization was modelled by the equation
y= 25520x+2657760
and showed that the values were still inflated, butregarding the uncertainty, some values reached the accepted value.
The reasons of such weak results were theuncertainties of the procedure, and old equipment. The scientist didn’t have aset time to start timing the boiling water, therefore the time could be thereason of the misleading calculations. The scales that the scientist wasusingwere three-beam, and not electronic. This could as well be a reason of theuncertain mass. It was difficult for the scientst to measure the exactmoment,when the water had evaporated 50 grams of water.
Reasonable improvements for this experiment wouldbe, setting a time for the scientist to start measuring