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Alcohols as fuels.

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Alcohols as fuels Introduction: Alcohols, as most of us know burn quite well in air (they react with oxygen when heated in air). This means we could use alcohol as a fuel to produce energy, as the reaction with air is exothermic. What effect would using different alcohols as fuels have? We might expect to find that larger alcohol molecules could be burned to give out larger amounts of energy, as the structure contains more chains of molecules which can react with oxygen to release more energy. In this investigation, we shall test a range of alcohols to see how much energy each releases when combusted. Plan: We shall be investigating how different alcohols give out different amounts of energy when burnt in air. We shall be using methanol, ethanol, propanol, butanol and pentan-1-ol in this investigation. The best way to perform the experiment to find out how much energy is given out by each alcohol is to use alcohol burners. These are short glass cylinders which are sealed off at the top. They have a short piece of rope reaching from the bottom of inside the burner (where the alcohol would be) to a hole with a metal ring at the top of the burner. The metal ring can be taken off with the rope to refill the burner. We shall use these alcohol burners to heat up a metal beaker of 50ml of water by 40�C. We shall use a thermometer to measure this heat change. ...read more.


Butanol gives nearly one thousand kJ mol-1 more than propanol and has 4 carbon atoms. Butanol gives out the most energy during the combustion of one of its molecules. From these calculations using theoretical values for bond energies from my chemistry book, ("GCSE Chemistry" by B. Earl & L. D. R. Wilford), I am able to predict which alcohol will be the most productive in terms of energy. The following graphs show what I predict will be the outcome of these experiments: As we can see, I think the mass difference between before and after weights shall decrease as we use alcohols with more carbon atoms in one molecule. As I have said, this is because the bonds produce more energy when there are more of then, more energy than the bonds take to break. Results: Methanol Mass (g) before After (g) before Difference (g) 1. 109.56 108.16 1.4 2. 108.13 106.92 1.21 3. 106.83 105.5 1.33 Ethanol 1. 111.7 110.52 1.18 2. 113.29 112.29 1 3. 112.24 111.12 1.12 Propanol 1. 113.08 112.44 0.64 2. 112.42 111.69 0.73 3. 111.64 110.95 0.69 Butanol 1. 116.94 116.05 0.89 2. 116.03 115.24 0.79 3. 115.22 114.35 0.87 Pentan-1-ol 1. 116.05 115.3 0.75 2. 115.28 114.62 0.66 3. 114.6 113.92 0.68 Methanol Ethanol Propanol Butanol Pentan-1-ol Average difference (grams) 1.31 1.1 0.69 0.85 0.70 Using the formula below, I can roughly see how much energy was needed to raise the temperature of the water by burning different alcohols. ...read more.


Also, the average difference for propanol and pentan-1-ol was very similar - the difference between these two results was a mere hundredth of a gram, showing them to be almost exactly the same in terms of heating up 50g of water. I have worked out the efficiencies of our experiments, and on average they were about 30% efficient. This was unavoidable due to the limitations in our abilities and equipment. The experiment could have been made more efficient using a bomb calorimeter. Calorimetry is the science of measuring a quantity of thermal energy in the process of heat transfer. A calorimeter is an instrument used to measure the amount of thermal energy; one widely used type consists of an insulated container of water, a stirring device, and a thermometer. A heat source is placed in the calorimeter, the water is stirred until equilibrium is reached, and the rise of temperature is noted by reading the thermometer. Because the heat capacity of the calorimeter is known, (or can be measured by using a standard heat source) the amount of energy given out can be easily calculated. When the heat source is a chemical reaction, such as the burning of a fuel, the reacting substances are placed in a heavy steel vessel called a bomb. The bomb is placed within the calorimeter, and the reaction is started by ignition with an electric spark. This would greatly increase efficiency as all heat would be used to heat the water. To further extend this work on alcohols, we could try using more alcohols, to obtain more results. Nicholas Moore 11Mc Group Q Mr Tansley 1 ...read more.

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