An Investigation into the Enthalpies of the Combustion of Alcohols Essa

An Investigation into the Enthalpies of the Combustion of Alcohols ================================================================== Planning My aim for this experiment is to see the energy produced from different alcohols. This investigation involves burning alcohol in the air. ‘GCSE Chemistry’ by B.Earl and L.D.R Wilford says that "alcohols form, another homologous series, with the general formula Cn H2n+1OH ". The alcohol reacts with the oxygen in the air to form the products water and carbon dioxide. This reaction is exothermic, as heat is given out. This is because the amount reactant energy is more than the product energy the difference between this is ΆH, therefore some energy has been given out in the form of heat. The energy is given out when forming the bonds between the new water and carbon dioxide molecules. This can be shown in an energy level diagram: Reaction co-ordinate ΆH is the heat content, which is the enthalpy, which is negative in exothermic reactions as the diagram shows that energy is 'lost' as heat. Enthalpy is defined as the energy of reaction, or the heat energy associated with a chemical change. For any reaction carried out directly at a constant pressure, the heat flow is exactly equal to the difference between enthalpy of products and that of the reactants. To measure the heat energy given off, we must use this energy to heat something, this will be water. This is assuming that all the heat produced by combustion of the alcohol will equal the amount of heat absorbed by the water (q). So I will measure the amount of energy required to do so. This can be worked out by using the formula: q = mass x specific heat capacity x temperature rise or q = MCΆH. Where q is the quantity of heat. The specific heat capacity is the amount of energy required to heat the substance, and is calculated using the formula: q =energy supplied/ Mass x Temperature, where q is the enthalpy, c is the specific heat capacity and ΆH is the temperature rise. I chose to use water as it is safe, easily obtainable, and has a constant, reliable specific heat capacity of 4.2J/ °C. The bonds which are made in a exothermic reaction are forces of attraction between the atoms or ions in a substance. These can be of two types: covalent, in which the atoms share electrons. Examples of this are water and carbon dioxide, whi... ...low temperature reading to heat the 100cm3 of water. The procedure of the experiment was good enough of finding out the energy gained from the individual alcohols, but changes could have been made to make the reliability of the results more accurate. This could have been done by using a better and more accurate thermometer, such as an electric thermometer, which have gave me a much more pin point set of results. If I were to do this experiment again I would make a number of improvements or changes, I could use a Bomb Calorimeter which submerges the reaction inside an insulated container of water. An electrical heating device starts the reaction inside a sealed reaction vessel and the temperature rise of the water which surrounds it is measured. Bomb calorimeters are often used to find the calorific value of foods. Looking at the experiment I did I thought we could have extended the results we achieved by using different flame lengths, this would have told us how much the alcohol uses its energy when the flame is increased. I could have also changed the amount of water in the copper calorimeter, or even change the concentration of alcohol to see the effect.