A defined amount of alcohol will be burned using a spirit lamp, to measure the energy change by measuring the change in water temp. As well as not wasting energy in the heating of the container, heat must be stopped from escaping around the edges of the container. To do this I would have to insulate the edge of the container by using the lid.
I predict that there would be a change in the amount of energy given off, getting greater, the more carbon atoms in the fuel, because the more there are, the more bonds to be made, thus producing more energy. The reactions that will take place are strongly exothermic, that is why they produce a colored flame. All of the reactions involve the alcohol and oxygen in the air reacting together to form water vapor and carbon dioxide. The formulae for the alcohols are below, with a general formula:
To deduce the amount of heat evolved the following formula will be used:
Heat Evolved = Mass x Specific Heat Capacity x Temperature Rise
The data collected in the experiment is given below:
Evaluation: more accurate results could have been achieved by modifying the experiment. The main causes for error in this experiment were:
1. Heat, which never enters the water, because of draughts.
2. Heat loss from the top and sides of the beaker.
3. Heat that is not conducted well by the beaker.
4. Incomplete combustion - there is a restricted supply of oxygen, the alcohol was burning with an orange flame rather than blue. Some of the alcohol did not burn completely, giving carbon and carbon monoxide rather than carbon dioxide. A carbon deposit (soot) on the bottom of the beaker indicated this.
5. Slight inaccuracies in the amount of water can greatly affect the end result.
6. Changes in the length of wick cause different amounts of alcohol burnt.
Improvements can be made to this by using a better insulation on the sides of the beaker, such as thick expanded polystyrene. Using a different material for the beaker, such as copper, which conducts heat more efficiently. By using a better lid and providing a draught screen with no gaps. This experiment has many sources of error, as the results were not exactly what were predicted. Things that can be improved to make a better investigation include using more results than just three to try to get rid of any uncommon results. Also I only used Alcohols that had the hydroxide group on the end, I could investigate using alcohols that have the hydroxide group in other places. I could use a much larger range of alcohols, going on to a higher range of carbon atoms, and investigate the differences between other organic substances such as hydrocarbons. There are also possibilities to investigate the burning of the alcohols under different temperatures or pressures.
