Comparing the Enthalpy Changes of Combustion of Different Alcohols

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. 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 from butanol as opposed to methanol because butanol has more bonds to be broken and made than methanol which has fewer bonds to be broken and made.

Method

I will use the following equipment to carry out my experiment:

• A copper calorimeter
• A thermometer
• 100cm….3 measuring cylinder
• Spirit burners containing

a) Ethanol

b) Methanol

c) Propanol

d) Butanol

• A balance
• A box (draught shielding)
• A stirrer

This is my method

1. Put 200cm…3 of water into a copper calorimeter and record its temperature
2. Weight the spirit burner you will use first
3. Support the calorimeter over the first spirit burner that you will test. Measure the distance from the bottom of the calorimeter to the top of the wick so it is always 10cm
4. Light the wick of the spirit burner
5. Stir the water all the time it is being heated. 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

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