Type of alcohol Energy required to break the bonds in the alcohol (j)
Methanol 2100
Ethanol 3270
Propanol 3740
Butanol 4560
Pentanol 5380
As you can see a longer molecule takes more energy to break its bonds, in this case Pentanol. Compared to a smaller molecule, methanol that 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. So when I come to predicting results I can safely say that Pentanol will evolve more energy than methanol simply because it has more bonds to break.
Set variable: I will be changing the type of fuel used.
Range of values: Methanol, Ethanol, Propanol, Butanol and Pentanol.
Measured variable: The outcome I will be measuring is the mass of fuel burned in grams.
Number of replicates: 3 times per fuel. There will be 15 altogether.
Controlled variables. To make sure the experiment will be a fair and reliable test, I will keep the following exactly the same every time the experiment is done; same distance between the burner and the can containing the water. Same temperature change in degrees centigrade. I will always use a foil shield placed around the burner to stop the wind blowing out the flame. Mass of water, 100cm. Type of container, tin. The same set of scales and always weigh the alcohol with the lid on.
Safety aspects: Tie long hair back, work standing up, never leave a flame unattended, turn flame off roaring after heating, tidy all other objects and work away.
Method: The method I used to conduct my experiment went as followed:
Measure 100cm of water in to a tin container.
Place the container into the grasp of the clamp stand.
Record the starting temperature of the water
Weigh the alcohol burner with the lid on.
Light the alcohol burner with a splint.
Put the chosen alcohol burner under the container allowing the flame to just touch the container.
Leave to heat up until the temperature of the water is exactly 20C more than the original temperature.
Weigh the alcohol burner.
Record all results.
Apparatus: The apparatus I used to conduct my experiment are as followed:
Alcohol burner containing different alcohols
Clamp
Tripod
Tin container
Foil
Weight scales
Measuring cylinder
Thermometer.
Average Mass used:
Heat energy released from 1g fuel:
Equation= 4.2 x Mass of water (100) x Temperature rise (20) divided-by Mass of fuel used up.
Butanol= 14237.28814
Methanol= 4352.331606
Propanol= 7850.46729
Ethanol= 6315.78974
Pentanol= 13125
Conclusion: The energy released by one mole of the alcohol increases proportionally when the number of carbons (and atoms) per molecule of alcohol increases. This supports my original prediction, that the more atoms per molecule of alcohol increases, the energy released will increase.
Evaluation: As I predicted, the energy released per mole of alcohol increased with the number of carbon atoms in each molecule of alcohol. This is because there are more bonds in the alcohols with more carbons per molecule than in the alcohols with fewer carbons per molecule.
When energy is put in, the bonds are broken. For the bonds to form again, energy is given out, and the amount of energy given out in the reaction is greater than that put in, meaning the reaction is exothermic. This means that to start the reaction, you need energy. Once the reaction is started, you get more energy back than you put in. This means that if you put more energy in, you get more energy out. You need more energy to break the bonds of Pentanol than Methanol, so you will get more energy out of burning Pentanol per mole, that you will with burning Methanol per mole.
Overall the experiment went well for me, even though the results could have been more accurate had I used foil to protect my flame and heat loss. I’m glad that I didn’t use foil however, as it gives me something to change next time and improve on in further experiments.
By Tom Spence 11H.