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To Determine the Enthalpy of combustion of different alcohols.

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Introduction

To Determine the Enthalpy of combustion of different alcohols. Skill Area P: Planning Prediction: I predict that as the number of carbon atoms in the alcohols increases, the enthalpy (or heat content) increases at a fairly equal rate. Detailed Scientific Knowledge: For any reaction to take place bonds must be broken and made, bond breaking requires energy while bond making releases energy. Bonds between different atoms require or release different amounts of energy when broken or made because the bonds are different in strength. The energy that is stored in chemical bonds is called enthalpy and given the symbol H. By looking at the equation for the reaction and more importantly looking at the bonds that are being broken and made, it is possible to work out an estimate for the amount of energy that will be released in the reaction. This is called the change in enthalpy. The enthalpy of a reaction is the change in energy going from reactants to products. For exothermic reactions, the enthalpy is negative while for endothermic reactions, the enthalpy is positive. A negative value for the enthalpy, or ?H denotes that energy has been released into its surroundings, bonds have been made and therefore there is an increase in temperature. A positive value of ?H shows that energy has been taken in from its surroundings and bonds have been broken, as there is now more energy and also a decrease in temperature. ...read more.

Middle

Next before lighting the burner, I will weigh it and make a note of the reading, as this is necessary in determining the amount of alcohol used. I will then place the burner under the calorimeter and adjust its height so that it is exactly 5 cm away from the top of the burner. I will take the temperature of the water and make a record of this, as this is necessary in calculating the temperature rise. After lighting the wick of the burner away from the calorimeter, the burner should be placed under the calorimeter quickly to stop unnecessary burning. I will stir the water at regular intervals of about every 5 seconds so that the temperature of the water remains constant everywhere in the beaker. Every 5 seconds or so I will check the thermometer to see whether the temperature is 40 oC higher than the initial temperature. When the temperature reaches that designated temperature, then I will stop the alcohol burner. Very carefully as the copper calorimeter would still be very hot, I would slide the burner from underneath and place it on the measuring balance. I would record this mass so that I would know the amount of alcohol used. The next thing that I would do would be to repeat this experiment again with the same alcohol for at least another 2 times, or until the results are very similar. ...read more.

Conclusion

I will use an electronic measuring balance so that I would be able to very accurately record the mass of the alcohol burner to at least 2 decimal places. This would mean that my results would be very accurate as opposed to using other measuring scales. As I have already mentioned, I will make this experiment a fair test so that I will obtain as accurate and reliable evidence as possible. There are some aspects of the experiment that may go wrong therefore I will need to especially careful when attempting them. When reading the temperatures of the thermometer, I will need to be very careful that I look directly at the reading not at any angle as this may affect the readings that I obtain. Also I should be very careful in measuring the distance from the top of the burner to the calorimeter as this would also affect the results and the energy produced. After lighting the burner, I will need to put it very quickly under the water as if I don't do this then some of the burner may be used up without heating the water. This is another thing that may go wrong. I will need to make sure that the metal calorimeter has completely cooled down so that there would be no energy stored in it at the start of the next experiment. However as I am repeating all the experiments I believe that this will not be so much of a problem. Hopefully however, I think that the experiment will run relatively smoothly throughout. Alex Bowles 1 ...read more.

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