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Investigate the amount of energy liberated when different alcohols are burnt.

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Introduction

Investigate the amount of energy liberated when different alcohols are burnt. For this investigation I will be burning 5 alcohols to heat up a beaker of water placed above. The alcohols I will be burning are methanol, propanol, pentanol, heptanol and octanol. My aim is to find out how much energy is produced when burning these alcohols and whether the number of carbon and hydrogen atoms effects this. Alcohols react with oxygen from the air to form water and carbon dioxide. Alcohols general formula is Cn H n + 1OH and is defined as a series of organic homologous compounds. The reaction that is involved in burning alcohols is exothermic because it gives heat off. The energy is given out when the forming bonds between the water and carbon dioxide molecules. The amount of energy produced by the exothermic reaction can be calculated by using the general formula Mass x rise in temp x SHC (specific heat capacity-number of joules required to heat 1 gram of water by 1oC. The bonds that are formed in an exothermic reaction can be of two types, ionic and covalent. Ionic- the transfer of electrons from one atom to another. These are metals. Covalent- the sharing of electrons between atoms, completing it's outer shell. ...read more.

Middle

* Keeping the lid on the spirit burner The variable which must be changed * The type of alcohol Results So that I was positive that my results were correct, I carried out the investigation twice. This was so that I not only had one set of results but two, so that I could take an average and therefore hopefully have more accurate results. Alcohol Start weight of spirit burner (g) End weight of spirit burner (g) Weight difference (g) Length of time it takes water to increase by 10oC Methanol 16.155 15.883 0.272 2.23 Propanol 14.886 14.644 0.242 1.51 Pentanol 13.335 13.143 0.192 1.30 Heptanol 14.469 14.196 0.273 1.15 Octanol 15.074 14.993 0.141 1.09 Alcohol Start weight of spirit burner (g) End weight of spirit burner (g) Weight difference (g) Length of time it takes water to increase by 10oC Methanol 16.373 16.049 0.324 2.34 Propanol 14.978 14.673 0.305 2.00 Pentanol 14.668 14.468 0.200 1.50 Heptanol 15.563 15.384 0.179 1.42 Octanol 15.526 15.252 0.274 2.58 From the sets of results we cannot actually come to maybe conclusions with ease. Therefore I can look at the rmm which helps me to find out the number of kJ per mole in each alcohol. ...read more.

Conclusion

To collect heat, it is almost impossible not to loss any part of it therefore these experiment can never be totally accurate. I feel that the most limiting factoring the experiment is the convection of air and the water. Also during the experiment water will have been lost and therefore the reading will have been slightly inaccurate. I believe that if I wanted to improve the accuracy of this experiment I could have tested more alcohols. Despite already having clear results they would have been even more easy to confirm if I had other alcohols such and ethanol and butanol. Next time I repeat this experiment I will focus on reducing heat lost. Improving insulation techniques would be a valuable asset in 100% accurate results. Another error is that of incomplete combustion. Complete combustion occurs if there are lots of oxygen atoms available when the fuel burns, then you get carbon dioxide, carbon atoms bond with two oxygen atoms. If in the case of a limited supply of oxygen then you get carbon monoxide, each carbon atom can only bond with one oxygen atom. This is known as incomplete combustion. This is because the carbon monoxide can react to make more carbon dioxide. If I were to repeat the investigation I would improve the accuracy of my results, however I am satisfied with them. They have given clear evidence and I can draw conclusions from them. ...read more.

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