or further away which would either give the water more or less energy.
⋅ Stir the water so that it is heated evenly otherwise energy would only reach
parts of the water and depending on where you placed your thermometer you could
get different results.
Prediction
I predict that the more bonds there are holding the carbon, oxygen and hydrogen atoms together, more energy will be required to break them apart. For example Ethanol has the formula C H OH. In this formula you have five C-H bonds, one C-C bond, one C-O bond and one O-H bond. To separate these types of bonds you require a certain amount of energy which I will show in a table..
TYPE OF BOND ENERGY REQUIRED TO BREAK THE BOND(j)C-H 410C-O 360O-H 510O=O 496C=O 740C-C 350
To separate C-H bond you need to apply 410 joules of energy. There are five such bonds in ethanol so you multiply 410 by five to get 2050 joules. You do these calculations for all the other types of bonds that make up ethanol, add them all together and you get 3270 joules. All of the other alcohols can be broken up in this way. Below is a table showing the energy required to break up the bonds in each alcohol.
Type of alcohol Energy required to break the bonds in the alcohol (j)Methanol 2100Ethanol 3270Propanol 3740Butanol 4560As you can see a longer molecule takes more energy to break it ´s bonds, in this case Butanol. Compared to a smaller molecule, methanol which 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 Butanol will evolve more energy than methanol simply because it has more bonds to break.
Obtaining Results
The Alcohols are a series of related organic molecules where each member has the -OH (hydroxyl) group in the molecule. The general formula of an alcohol is: Cn H 2n+1 OH, where n is the number of Carbon atoms. The similarities in molecular structure make alcohols have physically and chemically similar properties. The table below shows a general increase in melting points and boiling points as the number of carbon atoms increases
Alcohols formulae and properties:
Methanol CH3OH Melting = -94 Boiling = 65
Ethanol C2H5OH Melting = -117 Boiling = 78
Propanol(Propan-1-ol) C3H7OH Melting = -126 Boiling = 97
Butanol(Butan-1-ol) C4H9OH Melting = -90 Boiling = 117(The names like propan-1-ol refer to the position of the -OH group on the carbon chain, the OH groups above are on the first Carbon atom, the "1" position)This table shows that I will need to investigate a series of different alcohols in my investigation. Ideally I would need at least 4 alcohols for a good range of results for comparison.
The complete combustion of an alcohol involves reaction with Oxygen to produce Carbon Dioxide and Water. The general formula for this reaction is:Cn H 2n+1 OH + (n+n/2)O2 ? nH2O + nCO2Balanced equations for each of the available alcohols that I will use are as follows:Methanol 2CH3OH + 3O2 --- 2CO2 + 4H2OEthanol C2H5OH + 3O2 --- 2CO2 + 3H2OPropanol 2C3H7OH + 9O2 --- 6CO2 + 8H2OButanol C4H9OH + 6O2 --- 4CO2 + 5H2O
Tables
Results
Burning of Methanol
CH3OH + 11/2O2 - CO2 + 2H2O
O -- H
|
H -- C -- H + O = O - O = C = O + H -- O -- H
|
H
2061 + 747.45 - 1610 + 1856 = 2808.45 – 3466 = 657.55Kj
Burning of Ethanol
C2H5OH + 3O2 - 2CO2 + 3H2O
H O -- H
| |
H--C--C -- H + O = O - O = C = O + H -- O -- H
| |
H H
3234 + 1494.9 - 3220 + 2784 = 4728.9 – 6004 = 1275.1Kj
Burning of Propanol
C3H7OH + 4.502 - 3CO2 + 4H2O
H H O H
| | | |
H-- C -- C -- C -- H + O = O - O = C = O + H -- O -- H
| | |
H H H
4407 + 2242.35 - 4830 + 3712 = 6649.35 – 8542 = 1892.65K
Burning of Butanol
C4H9OH + 6O2 - 4CO2 + 5H2O
H H H O
| | | |
H -- C -- C -- C -- C -- H + O = O - O = C = O + H -- O -- H
| | | |
H H H H
5580 + 2289.8 - 6440 + 4640 = 8569.8 – 11080 = 2510.2Kj
Total bond energy’s
Methanol 657.55 Kj
Ethanol 1275.1 Kj
Propanol 1892.65 Kj
Butanol 2510.2 Kj
The values that are shown here do go in a trend. The one with the least amount
of bonds (methanol) appears to give out the least energy and the one with most bonds (Butanol) appears to give out the most energy. This shows that more heat energy comes from Butanol than it does from all the other alcohols.
Evaluation
I believe my results were very inaccurate. Below is a list of reasons why it was an inaccurate experiment.
1. Energy given off through sound and light.2. Heat conducted and convected away through the air.3. Radiation of heat out into the atmosphere.4. The fact that the beaker gets hot.5. The rubber clamp transferred heat way.6. Heat may be take away through guts of wind.7. The fact that at higher temperatures, heat is lost faster to the air and out of the beaker, due to the bigger heat difference, making the higher temperatures more inaccurate, and making a shallower gradient on the graph.8. By incomplete combustion9. The amount of energy you give the alcohol originally.10. The availability of alcohol for the wick to burn, if not enough then the wick would burn not the alcohol which would give an inaccurate result.11. Evaporation of water so there will be less water to heat, making the water hotter. 12. The size of the wick.13. Not all of the water was the same temperature.14. The flame size changed due to the type of alcohol, hence it was a different distance away from the beaker each time.
Numbers 1 –– 10 would decrease the reading and Numbers 11 –– 14 would increase the reading.
The equipment that I used in this experiment was very inaccurate because heat is a bad way of transferring energy without any loss of it. Any molecule will conduct heat, radiation happens and can be reduced but not completely halts. I feel that the most limiting factor of the experiment is the convection of air and to a lesser extent, of water. Also during the experiment, some of the water will have evaporated, thus the water mass/temp reading will be altered.
I feel that this experiment could have been improved by using a wider range of alcohols such as Pentanol, hexanol and heptanol. This would give a better graph reading and a wider range of results to support a firm conclusion. On the other hand, if I had started below room temperature, so that the amount of energy gained, from room temperature might equal the energy lost at temperatures higher than room temperature. Next time reducing heat lost would be my main priority. Improving insulation techniques would be a valuable asset in obtaining the most reliable data I could.
Another error is that of incomplete combustion. Complete combustion occurs if there are lots of oxygen atoms available when the fuel burns, then you get carbon dioxide (carbons atoms bond with two oxygen atoms).
If there is a limited supply of oxygen then you get carbon monoxide (each carbon atom can only bond with one oxygen atom). This is when incomplete combustion has occurred. This is so because the carbon monoxide could react some more to make carbon dioxide. If the oxygen supply is very limited then you get some atoms of carbon released before they can bond with any oxygen atoms. This is what we call soot. Since heat is given out when bonds form, less energy is given out by incomplete combustion. So this is why it affects the outcome of the experiment. To overcome this problem, I would have to make sure a sufficient supply of oxygen was involved in the reaction.