Latent heat practical


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Latent heat practical

  1. 1. Specific Latent Heat of Vaporization PracticalResearch Purpose:To Measure the Specific Latent Heat of Vaporization of WaterData Collection and ProcessingMass of kettle without the lid = 504 ±1 gMass of Kettle with water =1242 g ± 1 gChange in mass before the temperature of the water reached the boiling point = 22 g± 2gPower of kettle = 625 WTemperature of water = 100°C± 2°Trials Initial Final kettle Mass loss Time elapsed Latent heat of kettle mass mass (± 2 g) during mass vaporization(J (± 1 g) (± 1 g) change (± .01s) kg−1)±1264251 1220. 1170. 50. 252.85 31600002 1161 1111 50. 259.36 32420003 1111 1061 50. 242.00 3025000Average Latent Heat of Vaporization of the Three Trials = 3140000 J kg−1±126425In trial four the time was recorded each time the mass dropped 10 g.Initial kettle mass (± 1 g) Final kettle mass (± 1 g) Time elapsed during mass change (± .01s)1040 1030 57:421030 1020 114:201020 1010 163:011010 1000 217:141000 990 264:24The raw data was the temperature of the water, the initial mass of the kettle, thefinal mass of the kettle, the time elapsed during the mass change, and the powerproduced by the kettle.The processed data is the mass loss and the latent heat of vaporization.
  2. 2. Notes on Uncertainties: The mass of the kettle by itself, the mass of the kettle withwater, the initial mass, and the final kettle mass were all measured by a digital scalethat measured to the nearest gram. Therefore, the uncertainties of these values hadto be 1 gram. The mass loss was constantly held at 50 grams, but in order to get thevalue 50 grams the final kettle mass was subtracted from the initial kettle mass.Since, these values were subtracted, the uncertainty of the initial kettle mass (1 g)and the uncertainty of the final mass (1 g) had to be added together in order toobtain the uncertainty of the mass loss, which is 2 g. The value on the back of thekettle was used to determine how many watts the kettle produced, thereforenegating the need for an uncertainty value. The temperature value was notnecessarily measured, but the experiment was started when the water began to boil,which means that the temperature had to be the boiling point of water, which is100°C. Assuming that the water may have begun to slightly boil right beforethe temperature reached the boiling point, the uncertainty of the temperaturecould roughly be around 2 °C, according to this students estimate.Sample CalculationsTo find Mass LossMass loss = initial mass of kettle – final mass of kettleMass loss = 1220 g – 1170 gMass loss = 50. gTo find Latent Heat of VaporizationTheoryEnergy supplied to test material = Energy received by water and beaker(P kettle )(t) = m L v(625) (252.85 ) = 1220 L v(625) ( 252.85 ) = L v 50.3160 J g−1 = L v(3160)(1000) =L v3160000 J kg−1= L vUncertainty calculation for Latent Heat of Vaporization
  3. 3. Uncertainty for time is negligibleUncertainty for mass = 2/50Uncertainty for mass = 4%Uncertainty for Power is not needed because it was taken from the apparatusUncertainty for Latent Heat = 4%Uncertainty for Latent Heat = (.04)(3160000)Uncertainty for Latent Heat = ± 126425 J kg−1To find Latent Heat using the slope of a Time against Mass graphTrial four was used to collect the time every time 10 grams of water was lost.This data was used to plot a time against mass graph.Slope of the graph =TimeMassSlope of the graph = 5.283 sg−1(P kettle )(t) = L v m(slope) (P kettle )= L v(5.283)(625) = L v3301 J g−1 = L v(3301)(1000) = L v3301000 ± 126425 J kg−1 = L vConclusion
  4. 4. This project’s purpose was to find the specific latent heat of vaporization of water.The literature value for the water’s latent heat of vaporization is 2260 kJ kg−1(2260000 J kg−1). In this experiment, the average of the results of trials 1, 2, and 3was 3160000 J kg−1and the result yielded by the graph in trial 4 was 3140000 J kg−1,showing that the experiment was fairly precise. The difference between the answeryielded by this experiment and the literature value is an astounding 860000 kg−1.One primaryfactor in causing this difference is thatthe uncertainty was very high (±126425 J kg−1), but this is somewhat to be expected with such a large answer.Also,the lid of the kettle was left off the kettle because the kettle with its lid on had toomuch mass to be measured by the equipment in the lab. Since the lid was off, heatcould have been lost and dissipated into the air, as well as some of the mass of watercould have been evaporated off. This could definitely explain why the literaturevalue and the values obtained by this experiment do not match up. This experimentand its purpose of determining the latent heat of vaporization has manyapplications. An example where this applies is cooking. Many times cooks will put asubstance in water in order to increase its boiling point so that they can heat thewater to very high temperature and cook food fast and efficiently without the waterevaporating. By knowing the latent heat of vaporization of water, cooks and chemistcould be able to determine the most efficient substance and smallest amount of thatsubstance needed to increase water’s latent heat of vaporization, which would allowthem to cook food at very high temperatures. If food is cooked at high temperaturesthen, it can be cooked faster making consumers and people happy.Several errors attributed the inaccuracy of the results of this experiment. One of theerrors that occurred was that the value of the power produced by the kettle wastaken from the label on the back of the kettle, which was 625 watts. The powerproduced by the kettle is probably not exactly 625 watts but could be slightly loweror less than the value printed on the kettle. This would have affected the experimentby giving it a larger value than it should have been, which is exactly what happenedin this experiment. This problem could be fixed by using an ammeter to measure thepower produced by the kettle. Another error that occurred was that heat was lostinto the atmosphere because the lid of the kettle was not on top of it. Also mass waslost because some of the water evaporated into the air. This error could havedecreased the result of the latent heat of vaporization because it would have helpedthe water to loose mass more quickly, making the time elapsed smaller. To fix this amass scale could be found that was large enough to measure the mass of the kettleand its lid, so that the lid could be placed on top of the kettle and the mass stillrecorded. Another way to improve this experiment is to do the method used in Trial4. Recording the time every time 10 g of mass is loss and plotting a time againstmass graph will help the experiment be more accurate.