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SIMPLE CALORIMETRY TO FIND THE ENTHALPY OF COMBUSTION OF ALCOHOLS

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Introduction

EXPERIMENT8: SIMPLE CALORIMETRY TO FIND THE ENTHALPY OF COMBUSTION OF ALCOHOLS Date: 23/11/2010 I. Objective: The purpose of this experiment is to estimate the enthalpy of combustion of an alcohol by using calorimetry. II. Introduction: Principle To work out the enthalpy change of combustion of the alcohols, the energy released must be measured. The simplest way of doing this accurately is to use the heat of combustion of the alcohol to raise the temperature of a known amount of substance with a known specific heat capacity. The rise in temperature of this substance can then used to work out the heat transferred to the substance. Thus, the enthalpy change of combustion of the alcohol can be estimated by assuming all the heat is transferred to the substance. In this experiment, water is heated by combusting the alcohols as specific heat capacity of water is known as 4.2 J g-1 K-1. The enthalpy change of combustion of an alcohol can be calculated as the temperature rise of water and mass of the alcohol used can be found. i.e. ...read more.

Middle

of Butan-1-ol -2670 kJmol-1 Enthalpy of combustion of Butan-1-ol found in the experiment -2550 kJmol-1 In general, the standard enthalpy of combustion of alcohols found were lower than the literal value. Precaution The mass of water should not be too large or too small. If the mass of the water is too small, the heat absorbed by the apparatus will become greater proportion. If the mass of water is too large, the heat evolved by combustion of alcohols raise the temperature slowly and the heat loss to the surroundings will become large. Thus the mass of water used in this experiment is 300cm3. Initial temperature must be steady. i.e. room temperature. Temperature rise employed is around 15?. As there is heat loss to surroundings, large jumps in temperature would not show up as high as they should. The temperature rise cannot be too high. However, if the temperature is too low, it leads to great inaccuracy as there is measuring error in weighing the alcohol used, measuring the mass of water used and the temperature increase of water (reading the thermometer). ...read more.

Conclusion

The purity of Propan-1-ol may be the lowest among the three samples. Thus, the difference between the experimental and literal value of the enthalpy of combustion is the largest. Improvements 1. Minimize heat loss to the surroundings by placing a lid and insulating materials on the aluminium can. 2. Reduce heat carried away by air current from the spirit burner by placing shields around the apparatus 3. Find the heat capacity of the apparatus by electrical heating method. 4. Use Beckmann thermometer for higher accuracy in reading temperature. 5. Record the temperature at regular interval and plot graphs of temperature against time. Find the change in temperature by extrapolation to minimize the error in heat loss to the surroundings. 6. Use flame calorimeter instead. 7. Ensure the purity of the alcohols before carrying out the experiment. 8. The experiment should be carried out immediately as alcohols are volatile. V. Conclusion The standard enthalpy of formation of combustion of Ethanol was found to be -1120 kJmol-1 The standard enthalpy of formation of combustion of Propan-1-ol was found to be -1840 kJmol-1 The standard enthalpy of formation of combustion of Butan-1-ol was found to be -2550 kJmol-1 ?? ?? ?? ?? Name: Cheng Cheuk Hei Class: F6B (17) 1 ...read more.

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