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Enthalpy of Combustion Lab Report

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Introduction

22/9/2008 Dhruva Mahimtura Enthalpy of Combustion of Ethanol Aim: The aim of the following experiment is to determine the enthalpy change of combustion of ethanol when one mole of ethanol is burned completely with the help of a spirit lamp for a time period of one and a half minutes. Background: Specific Heat Capacity is the amount of heat required to raise the temperature of 1g of a substance by 1K. ? � Differs from substance to substance. ? � Water = 4.18 J g-1 K-1? � Ethanol = 2.4 J g-1 K-1 The data booklet value for the standard enthalpy of combustion of ethanol is -1371 KJ/mol. Apparatus: Instrument / Chemical: 1. Spirit lamp containing ethanol 2. Copper Calorimeter 3. Distilled Water 4. Stop Watch (?0.01s) 5. 1?50cm3 beakers 6. Retort Stand 7. Digital Thermometer (?0.1) 8. Digital Electronic Balance (?0.01g) 9. Stirring rod Method: 1. The mass of the spirit lamp containing ethanol is first determined accurately with the help of the digital electronic balance and is recorded as M1 (?0.01g). 2. Then a copper calorimeter is taken and the mass of the empty calorimeter is first determined. Then the calorimeter is filled with distilled water and the mass of the calorimeter along with water is then recorded. The two readings are then subtracted to determine the mass of the distilled water used in the experimental procedure with the help of the digital electronic balance and is recorded as M3 (?0.02g). 3. Then the calorimeter containing the water is placed on top of the retort stand and the digital thermometer is used to ...read more.

Middle

Raw Data: Initial mass of spirit lamp = M1, Final mass of spirit lamp = M2, Mass of distilled water used in the experimental procedure = M3, Initial temperature of water = T1, Final temperature of water = T2, The following table N1 shows the raw data that has been recorded in order to determine the enthalpy change of combustion of ethanol while conducting the following experimental procedure: Sr. No. M1 (?0.01g) M2 (?0.01g) M3 (?0.02g) T1 (?0.1) T2 (?0.1) 1. 168.50 166.85 121.16 - 42.94 = 78.22 27.2 38.2 2. 166.85 165.61 121.02 - 42.94 = 78.08 37.4 45.4 3. 159.00 157.50 126.26 - 43.53 = 82.73 26.5 36.2 4. 157.50 155.75 126.08 - 43.53 = 82.55 35.8 45.8 5. 155.75 154.44 125.83 - 43.53 = 82.30 44.3 51.1 Processed Data: Mass of ethanol that has been used and burnt completely = M1 - M2 = MF, Rise in Temperature of the distilled water when the spirit lamp is placed directly below the calorimeter = T2 - T1 = TF, The following Table N2 gives the values of the mass of ethanol that has been used and the change in temperature of the distilled water solution. Sr. No. MF (?0.02g) TF (?0.2) 1. 168.50 - 166.85 = 1.65 38.2 - 27.2 = 11.0 2. 166.85 - 165.61 = 1.24 45.4 - 37.4 = 8.0 3. 159.00 - 157.50 = 1.50 36.2 - 26.5 = 9.7 4. 157.50 - 155.75 = 1.75 45.8 - 35.8 = 10 5. ...read more.

Conclusion

3. It is assumed that the glass stirrer, the digital thermometer and the calorimeter were not absorbing any heat but in reality these instruments are also being heated. 4. It is assumed that none of the ethanol escaped through evaporation during the time the flame was extinguished and the spirit lamp and its contents were reweighed. However, ethanol is a volatile liquid and the fact that the spirit lamp was hot indicates that some of it would have evaporated. Conclusion: In the carried experimental procedure one has determined the enthalpy change of combustion of ethanol when one mole of ethanol is burned completely with the help of a spirit lamp for a time period of one and a half minutes. One has successfully proven the hypothesis that has been made earlier. I had predicted beforehand that the reaction-taking place in the experimental procedure is an exothermic one. The fact that heat is given out when ethanol is burnt has been depicted by the temperature rise of the distilled water present in the calorimeter. Hence it is clearly evident that the combustion reaction of ethanol is an exothermic reaction. Suggestions for Improvement / Evaluation: 1. There should not be any disturbance in the room where the experiment is being conducted as one is trying to prevent any interference to the internal system. 2. While conducting the experiment, one should use a shield like device in order to cover the entire apparatus and prevent any heat transfer between the surrounding and the internal system. 3. More efficient equipment should be used in the conducted experimental procedure. ...read more.

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