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Investigating enthalpy Change - During this investigation I will be burning a selection of different alcohol's to heat a container of water.

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Introduction

Investigating enthalpy Change During this investigation I will be burning a selection of different alcohol's to heat a container of water. I will be burning four alcohols, methanol, ethanol, propanol and butanol. The aim of the experiment is to find out how much energy is produced when these alcohols are burnt and to see if there's a relation between how many, and how strong the bonds are between molecules in the elements burnt, and how quickly the water is heated up. To put it simply, we will see if the enthalpy would increase per extra CH? added Any form of burning is an exothermic reaction; this means that heat is given out as a result. This means that the reactants energy is higher than that of the product. Alcohols react with oxygen in the air to form water and carbon dioxide. The energy is given out when new bonds are formed between the water and carbon dioxide molecules. The amount of energy produced by such exothermic reactions can be calculated by using this formula: Delta H is the amount of enthalpy (heat energy), M is the mass of the water, 4.2 is the specific temperature capacity of water (the amount of joules required to heat water by 1�C and Delta T is the waters change in temperature. ...read more.

Middle

For example Ethanol has the formula C H OH. In this formula you have five C-H bonds, one C-C bond, one C-O bond and one O-H bond (all of which are single bonds). To separate these types of bonds you require a certain amount of energy which I will show in a table. TYPE OF BOND ENERGY REQUIRED BREAKING THE BOND (kJ) C-H 410 C-O 360 O=O 496 O-H 510 C-C 350 C=O 740 To separate C-H bond you need to apply 410 joules of energy. There are five of these bonds in ethanol so you multiply 410 by five to get 2050 joules. You do these calculations for all the other types of bonds that make up ethanol, add them all together and you get 3270 joules. All of the other alcohols can be broken up in this way. Below is a table showing the energy required to break up the bonds in each alcohol. Type of alcohol Energy required to break the bonds in the alcohol (KJ) Methanol 2100 Ethanol 3270 Butanol 4560 Pentanol 6420 As you can see, a longer molecule takes more energy to break its bonds, in this case Butanol, compared to a smaller molecule, methanol, which requires less energy to do so. I can come to predict that the longer the molecular structure in the alcohol the more energy it will take to remove the bonds. ...read more.

Conclusion

Below are some possible reasons why my results were much lower than the theoretical values: o Some of the apparatus may have absorbed some of the heat energy given off by the fuel. Such as the beaker getting hot. o Some of the heat energy may have been taken away by gusts of winds or may have escaped into its surroundings. o Some of the water may have evaporated as a result of the high temperatures. This would mean that there would be less water to heat, making the water get hotter quicker. o The flame size changed due to the type of alcohol; hence it was a different distance away from the beaker each time. o And lastly incomplete combustion would have acted as a major factor into reducing the amount of energy release. I would not extend this investigation by experimenting with more alcohols as it is clear that the trend identified is likely to continue as long as the chain of molecules for each alcohol is increasing. I would extend this investigation by investigating other organic compounds, such as hydrocarbons, to see if they behave similarly. Likewise experimenting with the calorific values of different foods would also make good experiments. This is where the numbers of calories for each type of food will be measured and investigated. Michael South Bond Energy ...read more.

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