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Relationship between the increasing length of the carbon chain and the enthalpy of combustion of the alcohol that contains the carbon chain.

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Introduction

Relationship between the increasing length of the carbon chain and the enthalpy of combustion of the alcohol that contains the carbon chain. This experiment is carried out to determine whether there is a relationship between the increasing length of the carbon chain and the enthalpy of combustion of the alcohol that contains the carbon chain. If such a relationship arises can this information be used to predict the enthalpy change of combustion of any alcohol? This will hopefully be answered by the following experiment. The experiment will use known alcohols as heat source. The alcohol will be completely combusted this means that it will react with only the oxygen in the air to give carbon dioxide and water. Alcohols can be used as heat sources because they react exothermically. This means that when they react they give out more energy than they take in. In a reaction involving the complete combustion of an alcohol the bonds in that alcohol and the oxygen it is reacting with are broken. Energy is required for this to happen. These bonds then reform in a new order to make new compounds and chemicals in this case oxygen and water. ...read more.

Middle

This is the standard volume that all gasses occupy at room temperature and pressure (R.T.P) It was decided that the first four alcohols in the organic family would be used as the volume of oxygen required by the fifth to completely combust is more than the air can supply. This means that another source of oxygen would be needed for example a liquid oxygen tank. This is too expensive to be carried out in a school laboratory. This hypothesis from coursework.inf A theoretical value for the enthalpy change of combustion of each of the four alcohols can be worked out. This involves using the number and type of bonds and their corresponding bond energies. First the broken bonds are taken and worked out then the bonds that are made. As the bonds that are made give out energy this value is taken away from the value of the breaking bonds. This results in a negative number if the reaction is exothermic or a possitive number if it is endothermic. The energy released, as the carbon chain gets longer should increse. This is because there are more bonds to break and therefore more are made, this releases more energy. ...read more.

Conclusion

Alcohol Theoretical Values Values from Data book Methanol -679.55 -726.00 Ethanol -1297.10 -1367.00 Propanol -1914.65 -2021.00 Butanol -2535.20 -2675.60 The difference in the values shown, shows that the bond energy values used were only averages. An initial experiment was set up to investigate ways in which the experiment could be carried out in a more accurate and fair way. From this preliminary experiment it was determined that water would be placed in a copper calorimeter and placed above the spirit burner, ceramic heat mats would be used as draught excluders. It was also decided that the thermometer would be clamped with the bottom in the middle of the water and a stiring rod would be used to stir the water. This was so that the thermometer was not in contact with the calorimeter because if it were it would give the temperature of the calorimeter not the water. A copper calorimeter was chosen over a glass one because it conducted the heat through and into the water quicker and better. This was found when the two systems were tested. The possitioning of the copper calorimeter was chosen to be above the spirit burner instead of aside it, because heat rises so there would be a greater degree of error if it were placed to the side. ...read more.

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