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To Find Out Which of the Five Alcohol’s Makes the Best Fuel To Heat Water.

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Introduction

Investigation Aim: The aim of this investigation is to find out which of the five alcohol's makes the best fuel to heat water. Background Knowledge: Combustion - This is when you set alight a fuel to react it with oxygen. Complete Combustion - This happens when all of the fuel is combusted with the oxygen. A large/unlimited supply of oxygen is needed for Complete Combustion to take place. Incomplete Combustion - This happens when only some of the fuel is combusted with the oxygen. A blockage of fresh oxygen has prevented all harmless carbon dioxide gas from being formed and some poisonous carbon monoxide is formed. Organic Fuels - These are natural stores of chemical energy. When they are set alight they give off carbon dioxide and water. For complete combustion there should be enough oxygen available for the fuel to react with. An Endothermic Reaction is when more energy is needed to break bonds between atoms than is released when new bonds are made. An Exothermic Reaction is when more energy is given out in bond forming when compared to the amount of energy taken in to break the bonds between each atom. Oxidation (combustion) is an Exothermic Reaction. Preliminary Work: Aim: To find out how much the temperature changes of water of volume 40cm3 in two minutes after being heated by ethanol. Method: We will use the following equipment: Ethanol Alcohol Burner Boiling Tube Clamp Stand Stop watch Measuring Cylinder Thermometer We will set up the equipment as shown: We will put the ethanol into the alcohol burner and set it alight. ...read more.

Middle

We are going to keep the lid on the top of the burner at all times so that no fuel is lost due to evaporation. We are going to change: The type of fuel. Prediction: We think that methanol will be the least efficient for heating water, alcohol out of the five I mentioned above. To prove my prediction we will calculate the amount of energy released ?H is when the alcohol reacts with oxygen. Methanol Reactants: energy is needed to break the bonds. We will use the following bond energies. C - H 412kJ/mol C - O 360kJ/mol O - H 463kJ/mol C = O 743kJ/mol O = O 496kJ/mol C - C 347kJ/mol (C-H x 3) + C-O + O-H + (O=O x 3/2) 1236 + 360 + 463 + 744 = 2803kJ/mol Products: energy is given out to form bonds. (4 x O-H) + (C=O x 2) (4 x 463) + (2 x 743) 1852 + 1486 =3338kJ/mol ?H = Reactants - Products. 2803 - 3338 = -535kJ/mol Ethanol Reactants: energy needed to break the bonds. (C-H x 5) + C-C + C-O + O-H + (O=O x 3) (5 x 412) + 347 + 360 + 463 + (3 x 496) = 2060 + 347 + 360 + 463 + 1488=4718kJ/mol Products: energy given out to form bonds. (6 x O-H) + (C=O x 4) (6 x 463) ...read more.

Conclusion

My graph shows that the smaller the alcohol, the less energy it gives out. Methanol needed the least energy to break the bonds but it only released a slightly bigger amount of energy when new bonds were formed. The larger the alcohol, the larger the differences in reactant and product energies and the more exothermic the reaction is. Evaluation: On my graph, the first four alcohols on my actual ?H line gave a good relationship between ?H and the amount of carbons. The butanol had a much higher ?H than expected. All my actual ?H was lower than my predicted ?H. This was because in my experiment energy was lost to the surroundings and not all of it was transferred to the water. I could try to improve the experiment to reduce energy loss by lowering the boiling tube so that it is closer to the flame or prevent the wick itself from being burned. Think that the butanol was higher than the others were because the experiment had to be done in a fume cabinet because of safety reasons. The fume cupboard takes out toxic gases and brings in more air. This could improve the rate of reaction, as there is more oxygen to be combusted and release more energy. The only way I could improve this test is by doing all of the alcohols experiments in the fume cupboard. To extend this experiment further I could look at other organic series to see if the same relationship between molecule size and ?H exists: e.g. Alkanes (Methane, Ethane and Propane). ...read more.

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