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Investigate how the amount of heat produced by burning a fuel depends on the mass of fuel burned.

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SKILL AREA P: PLANNING Aim To investigate how the amount of heat produced by burning a fuel depends on the mass of fuel burned. Hypothesis I predict that the amount of heat energy produced by burning the fuel (we are using ethanol) will be proportional to the mass of ethanol burned. I have based this prediction on the following scientific knowledge (as suggested in a secondary source - 'Chemistry: A Practical Approach' by A.L Barker and K.A Knapp): Within the reactant molecules of a chemical reaction, there are many tiny atoms which are held together by very strong forces. These forces which link atoms in molecules together are called bonds. All chemical reactions consist of bonds in the reactant molecules being broken, and new bonds being formed. The chemical reaction that I am investigating is that of ethanol burning in oxygen to produce carbon dioxide and water, and this idea of bonds applies here too. 'It is impossible to measure the total energy stored up in a particular substance, but we can measure the change in it which occurs during a chemical reaction. The symbol used for such a change is H where (delta) means 'change of' and H is the 'heat content' or enthalpy of the system.' An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat, and because of this, H is positive because the system gains energy from the surroundings. Energy must be supplied to break existing bonds, so bond breaking is an endothermic process, whereby energy is gained from the surroundings. In an endothermic reaction, the energy required to break old bonds is greater than the energy released when new bonds are formed. In contrast, an exothermic reaction is one which gives out energy to the surroundings, usually in the form of heat, therefore H is negative for an exothermic change because the system loses energy to the surroundings. ...read more.


My first experiment was to decide what would be the ideal amount of tap water to use in the can, so as to perform an accurate yet safe final investigation, bearing in mind the time restrictions. I used a spread of volumes of water (between 50 - 150cm3), and for each, I obtained results for a selection of masses of ethanol (1g, 3g, and 5g). I chose these masses because they would provide me with a wide range of results of the maximum temperature reached with these volumes of water. I have demonstrated these results in the table below: Amount of water (cm3) Initial Temp. (?C) Final Temp. (?C) 1g ethanol 3g ethanol 5g ethanol 50.0 22.0 69.0 99.0 110.0+ * 100.0 22.0 45.0 74.0 99.0 150.0 22.0 33.0 59.0 78.0 *Although the temperature was continuing to rise at this point, the scale of the thermometer did not surpass 110?C, and thus I was unable to record any further. These results show me that when the amount of water in the can is 50.0cm3, the temperature of the water rises very rapidly, even when the mass of ethanol is small. We can see that when using 5g of ethanol, the water temperature rises too high even to be calculated with the equipment I have, and for this reason, it would be unwise to choose this volume of water to conduct my experiment with. At the same time, these results show that when the amount of water in the can is 150.0 cm3, the temperature of the water rises slowly, with the highest temperature reached being only 78?C, as opposed to the 110+?C obtained when the volume of water is 50.0cm3. For this reason, this data may not offer me the variety I would need to deduce a trend in the results, and thus I will not use this volume of water in my experiment. ...read more.


This also explains why my preliminary results show a straight line of best fit and thus do support my prediction, as opposed to my final results: in my preliminary investigation, I only experimented with 0.0-3.0g of ethanol, with the highest temperature reached being only 63?C, and thus the fuel did not begin to boil, as in my final experiment. Hence for this reason, the heat energy derived from burning the ethanol at this point was not all being used for breaking bonds, but also for raising the temperature, and so in this preliminary experiment I found the relationship I had expected: heat produced ? mass of ethanol burned. Judging from my final results, we can assume that had I increased the mass of ethanol in my preliminary results beyond 3.0g, this graph would too have demonstrated a curve of best fit. SKILL AREA E: EVALUATING EVIDENCE As mentioned previously, I can see from the several anomalous results in my graph that there must have been flaws in my experiment, thus in this way I resulted in some erroneous data. The reasons for these errors could be: * Measuring the distance between the base of the can and the crucible - in collecting the data, I was slightly pushed for time and hence would not have been very careful in measuring this distance. * Using a measuring cylinder to measure out the 100cm3 of water - it was not entirely accurate, so I should have used either a burette, or if not then a pipette to be more precise. * Drawing my graph by hand - I should have used a computer to reduce the chance of human error. Having concluded thus, I could extend this experiment further now. To do this I would experiment with different alcohols such as Butanol and Methanol. CHEMISTRY An investigation into how the amount of heat produced by burning a fuel depends on the mass of fuel burned NOOR NANJI CANDIDATE NO. 8216 SOUTH HAMPSTEAD HIGH SCHOOL CENTRE NO. 10264 1 ...read more.

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