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What energy do fuels liberate when burnt?

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What energy do fuels liberate when burnt? Substances are held together by chemical bonds. When a chemical reaction occurs, one substance changes to another. This means that chemical bonds must be broken and then re-made. It is the bond breaking and making that causes energy changes in chemical reactions. Before a reaction can begin, bonds have to be broken. Breaking bonds involves pulling atoms apart and this requires energy. At room temperature this energy is not available, so bonds do not break and the reaction does not begin. However, if you heat the fuel enough, energy is transferred to break the necessary bonds and the reaction begins. All reactions need activation energy to break bonds and get them started. For some reactions the bonds are easily broken. As a result the activation energy is fairly minimal and the reaction may even begin at room temperature. For example, the reaction of sodium with water. Other reactions need a lot of energy to break bonds and get them started. For example, charcoal (carbon) requires a vast amount of heat to get it to burn. This is because the bonds holding the carbon atoms together are very strong. Whenever chemical reactions occur, energy is transferred to or from the surroundings. ...read more.


* Copper pot * 50 cm3 of water * Balance scale Copper pot containing 50 cm3 of water Thermometer Boss & clamp Pole 10cm Balance scale Spirit burner Bunsen burner Heat proof mat Method Before I begin the experiment I will set up the required equipment as pictured in the diagram above. Once it is all in the correct place, I will begin by weighing the spirit burner with its lid on (containing either methanol, ethanol, propan-1-ol, pentan-1-ol or butan-1-ol). Once I have recorded the weight I will then place the spirit burner under the copper pot containing 50cm3 of water and remove its lid. With a splint lit from the Bunsen burner, I will then light the wick. As soon as the temperature of the water has increased by the desired amount (either 5?C, 10?C, 15?C, 20?C, 25?C or 50?C) I will replace the lid of the spirit burner and weigh it for a second time. Whilst I weigh the burner to find the change in mass, my partner Louise will replace the water in the copper pot with another 50cm3 of water. I will repeat this procedure three times for each fuel at each of the required temperature changes. ...read more.


The pattern that my results show is, the bigger the molecular size and bond energy changes, the lower the mass change and the bigger the energy change per gram and mole of fuel. From analysing my results I am able to conclude that the molecular size of a fuel effects the amount of energy that it liberates when burnt. The bigger the molecular size of a fuel, the smaller the mass that it will lose when burnt. This is because, the greater the molecular size, the more bonds there are to be broken and the bigger the bond energy change. Therefore the bigger the bond energy change, the more energy the fuel gives out to the surroundings in the form of heat and the smaller the mass of fuel required to heat 1 g of water by 1?C. My prediction was correct, the bigger the molecular size of a fuel, the smaller the amount of fuel it will take to heat 50cm3 of water by the required temperature. This is because the bigger the bond energy changes, the more energy that is lost to the surrounding area in the form of heat. My prediction was also correct because the mass decrease of the fuels followed the list below as predicted (biggest mass loss first): * Methanol (CH3OH) * Ethanol (C2H5OH) * Propan-1-ol (C3H7OH) * Butan-1-ol (C4H9OH) * Pentan-1-ol (C5H11OH) Amie Mustill ...read more.

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