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The aim of this investigation is to compare the enthalpy of the following different fuels:Ø Methanol - CH3OHØ Ethanol - C2H5OHØ Propanol - C3H7OHØ Pentanol - C5H11OH

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Aim: The aim of this investigation is to compare the enthalpy of the following different fuels: > Methanol - CH3OH > Ethanol - C2H5OH > Propanol - C3H7OH > Pentanol - C5H11OH Background Information Crude oil (petroleum) is our main source of food and organic (carbon-based) chemicals. Crude oil is a thick, smelly, dark brown liquid. It is a mixture of hundreds of compounds. These vary from simple substances like methane (CH4) to complex substances with dozens of atoms per molecule. Most of the compounds in crude oil are hydrocarbons. Crude oil itself is useless. It must be separated into different fractions before it is used. Each fraction contains a mixture of hydrocarbons with similar properties. Some of the fractions contain volatile hydrocarbons, which are easily vaporized. These fractions can be used as petrol. Other fractions are much less volatile. They can be used as fuel for ships and power stations. A furnace first heats the crude oil and the vapours pass into the lower part of the fractionating column. As the vapours rise up the column through holes in the trays, the temperature falls. Vapours of different compounds condense at different heights in the column as the temperature falls below their boiling points. Liquids such as petrol (gasoline), which boil at low temperatures, condense high up the column. Liquids such as diesel oil, which boil at high temperatures, condense lower down. Each fraction from crude oil contains a mixture of similar compounds with roughly the same number of carbon atoms. The uses of the various fractions depend on their properties. Fraction Boiling range/?C Number of carbon atoms in molecules Uses Refinery gas Up to 40 (below room temperature) 1- 4 Fuel for gas cookers, LPG, GAZ, plastics Petrol (gasoline) 40 - 140 (40?C) 5 - 10 Fuel for vehicles, chemicals Naphtha 140 - 180 (110?C) 8 - 12 Raw material for chemicals and plastics Kerosene (paraffin) ...read more.


= 10 x 346 = 3460 22(C - H) = 22 x 435 = 9570 2(C - O) = 2 x 336 = 672 2(O - H) = 2 x 464 = 928 30(O = O) = 30 x 497 = 14910 20(C = O) = 20 x 803 = 16060 24(O - H) = 24 x 464 = 11136 Total: 29540 KJ Total: 27196 KJ Two moles of pentanol releases: ?H = Bond Broken - Bond Formed = 29540 - 27196 = 2344 KJ One mole releases: 2344 2 = 1172 KJ/mol By using my background information, I can predict that the energy released increases as the chain length of an alcohol increases. This prediction is based on the bond energy calculations: the energy released per mole. This means that the fuels will come in the following order: Methanol, Ethanol, Propanol, Pentanol The above fuels have different boiling points so will boil at different temperatures due to different chain lengths. At higher temperatures, particles are moving faster, so there are more collisions. Also, and more importantly, the collisions are more energetic. More collisions have energy greater than the activation energy. The molar heat of combustion of a fuel is the amount released when one mole of a substance burns in the air. The graph below shows the relationship between the heat of combustion and a series of alkanes: Alcohol Heat of combustion, from data book (KJ/mol) Ethanol 1130 Propanol 2020 Butanol 2680 As shown, the increased heat of combustion seems to be associated with an increased number of atoms in the fuel. This is the reason how I made my prediction that the energy released increases as the chain length increases. This should also apply to the alcohols. Fair Testing To ensure that my experiment is fairly carried out I shall do the following: * I should not give priorities to one fuel only. ...read more.


This is because the amount of heat loss from the other practicals going on varied and inter-related with my experiment giving either more heat to it by giving a slightly higher temperature. This means that I could not keep my temperature variable constant. Conclusion The aim of my investigation was to compare the enthalpy of four different fuels. My book values were very high and so were my predicted values. My practical results did not show a relationship due to the conditions in the laboratory by other same practicals taking place. Therefore, their heat loss affected my results. This means that my results are not firm enough to draw a conclusion as the conditions in the laboratory affected my results by varying them. This is shown not only in my results but also in my graph and my calculations. Evaluation To improve my experiment I could do quite a lot of things. Firstly, I could have used a calorimeter and an insulated lid on top to prevent heat loss. All the windows should have been closed so that the heat could not escape outside. The experiment should not have been carried out near a window as I was allowing extra heat in. I should have used the same balance, as different balances have different values. It was good that I used height blocks to get the spirit lamp underneath the beaker. For extra prevention I used aluminium foil so that the heat reflected back to the calorimeter. This was good. I also used height blocks to minimise heat loss and tried to put the spirit lamp under the beaker. However, the spirit lamp was not directly under the beaker. I felt that it was good that I took a range of readings by getting two sets of results then taking the average. This improved the accuracy of my results. However, I could have taken a second opinion of the readings. By asking someone else what reading they saw I could see whether I made a mistake in my reading and from some of my results I see that I have made mistakes. ...read more.

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