Comparing the Enthalpy Changes of Combustion of Different Alcohols :: Enthalpy

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 - 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. Otherwise different amounts of energy could escape each time making it an unfair test. Plan: From carrying out the follow experiment I will be able to find out the enthalpy change of each fuel I am testing. The enthalpy change of combustion of a fuel is the measure of energy transferred when one mole of fuel burns completely. I will use the fact that 42 Joules of energy are required to raise the temperature of 1 gram of water by 1 C. Enthalpy change varies according to the following conditions – temperature, pressure and concentration of solutions. Therefore I will use a standard pressure of I atmosphere, a standard concentration of 1 mol dm†¦.3 and finally a specified temperature of†¦. I will use the equation enthalpy change = cm†¦..T c- Specific heating capacity of water m- Mass of water in grams †¦T- Change in temperature of water I will then compare 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.