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# Comparing the Enthalpy Changes of Combustion of Different Alcohols

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Introduction

Comparing the Enthalpy Changes of Combustion of Different Alcohols Aim: I will find the enthalpy change of combustion of a number of alcohols so that I can investigate how and why enthalpy change is affected by molecular structure of the alcohol. Outline: I will use Methanol, Ethanol, Propanol and Butanol in the experiment. I will use these four because they should give me clear results, and they range from short chained to long-chained hydrocarbons, so patterns should be easy to spot in the conclusion. Variables: My independent variables are - The type of alcohol (I will use ethanol, methanol, propanol and butanol) My dependant variables are - the specific heating capacity of water - Mass of water in grams ...T- Change in temperature of water My control variables are - The change in temperature of water- 20..C - The mass of water. If this were changed then all the results would be wrong, because it would take different amounts of energy to heat different volumes of water - The distance from the bottom of the calorimeter to the top of the wick. ...read more.

Middle

the enthalpy changes and the types of molecular structures and so I will able to out why enthalpy change is affected by the molecular structure of the alcohol Prediction: I predict that as the number of carbons in the alcohol is increased, the enthalpy of combustion also increases. The enthalpy change of combustion of alcohols increases as the length of the chain increases. This can be explained if we compare one alcohol with the next in the series. The chain length increases with an addition of a CH2 group. When the alcohol is combusted what actually happens is the covalent bonds are broken, and new bond are formed. More energy is released from the formation of bonds then is absorbed to break the bonds of the alcohol. So the more atoms in the alcohol, more bonds are broken, and more bonds are formed. The enthalpy change of combustion of different fuels is affected by their molecular structure because it takes more energy to break and make bonds ...read more.

Conclusion

Heat the water until the temperature has raised by 20...c 6) Extinguish the burner, stir the water and record the highest temperature reached 7) Weigh the burner to find out the mass of fuel that has been burned 8) Repeat the above process using the other alcohols. 9) Record the results in to the following table 10) Repeat the experiment twice to find a average result to make it more accurate 11) Use these results to find out the enthalpy change of combustion Type of fuel Temperature of water to be heated Weight of spirit burner Before Highest temperature of water reached Weight of spirit burner After Methanol Ethanol Propanol Butanol Risk Assessment: I will be using spirit burners so I must be careful that I do not spill fuel anywhere, because it highly flammable and is a fire hazard. I will wear safety goggles so that I do not get anything in my eyes and I will also wear a lab coat. I must not be careful with the calorimeter after it has been heated as it will be very hot ...read more.

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