The Combustion of Alcohols
Ryan McCarley
GCSE Chemistry Coursework
The Combustion of
Alcohols
Aim)
My aim in this is experiment is to see how good a fuel alcohol is.
Background Knowledge)
Combustion is the rapid chemical reaction between substances that is usually accompanied by generation of heat and light in the form of flame. In most cases, oxygen comprises one of the reactants. Other physical phenomena that sometimes occur during combustion reactions are explosion and detonation. Combustion, one of the most important classes of chemical reaction, is often considered a climax phenomenon in the oxidation of certain types of substances. Although most flames have regions where reduction reactions are important, combustion is primarily the combining of combustible material with oxygen.
Chemical and physical aspects)
The chemical processes in combustion are most commonly initiated by such factors as heat, light, and sparks. As the combustible materials achieve the ignition temperature specific to the materials and the ambient pressure, the combustion reaction begins. The combustion spreads from the ignition source to the adjacent layer of gas mixture; in turn, each point of the burning layer serves as an ignition source for the next adjacent layer, and so on. Combustion terminates when equilibrium is achieved between the total heat energies of the reactants and the total heat energies of the products. Combustion may be propagated by complicated branched-chain reactions, as in hydrogen combustion. Other types of reactions, such as the combustion of carbon monoxide, are characterized by a fast interaction step between a hydroxyl radical (OH) and the carbon monoxide molecule (CO). Although the mechanisms of hydrocarbon combustion are not completely known, many of the steps involving hydrogen and oxygen atoms and hydroxyl and organic radicals are similar to those for hydrogen and carbon monoxide combustion. In addition to the chemical processes in combustion, physical processes that transfer mass and energy also occur. In gaseous combustion, for example, the diffusion of reactants and combustion products depends on their concentrations, pressure and temperature changes, and diffusion coefficients. Convection, which is also responsible for the transport of mass and energy, comprises buoyant and external forces, and turbulent and eddy motions. Combustion may also emit light energy, mostly in the infrared portion of the spectrum. The light emitted by a flame arises from the presence of particles in electronically excited states and from ions, radicals, and electrons.
Explosions)
An acceleration of a combustion reaction, whether caused by a rise in temperature or by an increase in the lengths of reaction chains, can lead to an explosion. In the former case a thermal explosion will occur when the rate of heat released by the reaction exceeds the rate of heat lost from the area. In the latter case a so-called chain explosion will occur when the probability of chain branching equals that of chain termination. When a combustion reaction accelerates progressively so that the flame front area advances at a supersonic velocity, compression from the shock wave causes an increase in temperature that results in self-ignition of the fuel. This phenomenon, called detonation, will not occur when energy loss from the reaction zone exceeds a certain limit.
Complete combustion- this occurs when there is a good supply of oxygen and all the fuel burns.
Hydrocarbon + Oxygen --> Carbon Dioxide + Water
(Good Supply)
Incomplete combustion- this occurs when there is a poor supply of oxygen (e.g. air) and not all the fuel burns.
Fuel + Oxygen --> Carbon + Water + Carbon + Carbon
(Poor Supply) Dioxide Monoxide
Alcohols-
Any of a class of organic compounds characterized by one or more hydroxyl (OH) groups attached to a carbon atom of an alkyl group (hydrocarbon chain). Alcohols may be considered as derivatives of water (H20) in which one of the hydrogen atoms has been replaced by an alkyl group. Alcohols are among the most common organic compounds and are valuable intermediates in the synthesis of other compounds.
Most alcohols are colourless liquids or solids at room temperature: primary alcohols with fewer than 12 carbon atoms are liquid; those with 12 or more carbon atoms are solid. Polyhydric alcohols (those with more than one hydroxyl group) usually have the consistency of syrup. Alcohols with complex arrangements of carbon atoms, such as sterols, are usually solids. Alcohols of low molecular weight are highly soluble in water. With increasing molecular weight, alcohols become less soluble in water and their boiling points, vapour pressures, densities, and viscosities increase.
Alcohols are among the more abundantly produced organic chemicals ...
This is a preview of the whole essay
Most alcohols are colourless liquids or solids at room temperature: primary alcohols with fewer than 12 carbon atoms are liquid; those with 12 or more carbon atoms are solid. Polyhydric alcohols (those with more than one hydroxyl group) usually have the consistency of syrup. Alcohols with complex arrangements of carbon atoms, such as sterols, are usually solids. Alcohols of low molecular weight are highly soluble in water. With increasing molecular weight, alcohols become less soluble in water and their boiling points, vapour pressures, densities, and viscosities increase.
Alcohols are among the more abundantly produced organic chemicals in industry. Some, such as ethanol and methanol, are utilized in great quantities. Ethanol, CH3CH2OH, also called ethyl alcohol, or grain alcohol, can be made by fermentation from the carbohydrates found in fruits, molasses, grains, and other agricultural products. It is also made industrially from ethylene, CH2CH2. Ethanol is used in toiletries and pharmaceuticals and to sterilize hospital instruments. It is, moreover, the alcohol in alcoholic beverages. The anesthetic ether is also made from ethanol.
Methanol, also known as methyl alcohol, wood alcohol, or carbinol, can be manufactured from hardwood or from hydrogen and carbon monoxide (CO). It is used as a solvent, as a raw material for the manufacture of formaldehyde and special resins, in special fuels, in antifreeze, and for cleaning metals. Methanol and ethanol are good fuels for automobile engines because they have high octane ratings and low pollution emission, though their solvent properties can cause problems by dissolving certain materials used in modern fuel systems. Gasohol, a solution of 10 percent ethanol in gasoline, is an alternative fuel that can be used in most automobiles without the solvency problem.
Methanol, also known as methyl alcohol, wood alcohol, or carbinol, can be manufactured from hardwood or from hydrogen and carbon monoxide (CO). It is used as a solvent, as a raw material for the manufacture of formaldehyde and special resins, in special fuels, in antifreeze, and for cleaning metals. Methanol and ethanol are good fuels for automobile engines because they have high octane ratings and low pollution emission, though their solvent properties can cause problems by dissolving certain materials used in modern fuel systems. Gasohol, a solution of 10 percent ethanol in gasoline, is an alternative fuel that can be used in most automobiles without the solvency problem.
Problems with Combustion)
The carbon dioxide that is given off during combustion is thought to be one of the causes of global warming. The CO2 allows the sun's radiation in, but it doesn't let the radiation back out. This trapped heat is causing the earth's average surface temperature to rise.
Preliminary Experiment)
The aim of the Preliminary Experiment was to find out that alcohol could be used as a fuel. In the Preliminary Experiment we set up the equipment in the same way as the Main Experiment.
? 1 Fuel Burner containing Ethanol
? 1 Boiling Tube containing 30cm3 of water
? 1 Thermometer
? 1 Clamp and Stand
? 1 Measuring Cylinder
We Used the Ethanol to heat up 30cm3 of water in a boiling tube 3 times.
From our results we saw that Ethanol was a good fuel and from our Preliminary Experiment we decided on several points for keeping the Main Experiment a fair test.
? Same distance between the flame of the burner and the bottom of the
boiling tube.
? Stir water in the same direction (clockwise) gently.
? 30cm3 of water.
We decided on using the following alcohols in our main experiment.
? Methanol (CH3OH)
? Ethanol (C2H5OH)
? Propan-1-ol (C3H7OH)
? Propan-2-ol (C3H7OH)
? Butan-1-ol (C4H9OH)
Prediction)
In this experiment I hypothesise that each fuel with give of energy in the form of heat and therefore heat up the water in the boiling tube.
I also predict that the more complex the fuel, and the more components in it, the greater the amount of energy that will be given off. I believe this because of the fact that it takes more energy to break all the bonds with the bigger alcohols between atoms but also a greater amount is given off when the new bonds are formed, and so, the greater the size of the alcohol, the greater the amount of energy given off when the new bonds are formed.
The relationship between the size of the compound of the fuel and the amount of energy given off when new bonds form is that they are directly proportional to each other.
I will now work out the theoretical ? Hs for each fuel. This means I am going to work out the amount of energy that should be given off by each fuel.
These are my theoretical ? H:
Methanol:
(3 x 412) + 360 + 463 + (1.5 x 496)
= 2803 kJ/ mol
(2 x 743) + (4 x 463)
= 3338 kJ/ mol
2803 - 3338 = -535
=-535 kJ/ mol *
Ethanol:
(5 x 412) +347 +360 +463 +(3 x 496)
= 4718 kJ/ mol
(4 x 743) + (6 x 463)
= 5750 kJ/ mol
4718 - 5750 = -1032
=-1032 kJ/ mol *
Propan-1-ol:
(7 x 412) +(2 x 347) +360 +463
+ (4.5 x 496)
= 6633 kJ/ mol
(6 x 743) + (8 x 463)
= 8162 kJ/ mol
6633 - 8162 = -1529
=-1529 kJ/ mol *
Propan-2-ol:
(7 x 412) +(2 x 347) +360 +463
+ (4.5 x 496)
= 6633 kJ/ mol
(6 x 743) + (8 x 463)
= 8162 kJ/ mol
6633 - 8162 = -1529
=-1529 kJ/ mol *
Butan-1-ol:
(9 x 412) +(3 x 347) +360
+ 463 + (6 x 496)
= 8548 kJ/ mol
(8 x 743) + (10 x 463)
= 10,574 kJ/ mol
8548-10,574 = -2026
=-2026 kJ/ mol *
Fuel
Amount of energy given off
Methanol
-535 kJ/ mol *
Ethanol
-1032 kJ/ mol *
Propan-1-ol
-1529 kJ/ mol *
Propan-2-ol
-1529 kJ/ mol *
Butan-1-ol
-2026 kJ/ mol *
Note: *- the minus means the reaction is exothermic.
As you can see from my results, my prediction is proven as Butan-1ol is the biggest alcohol and I predicted that it would give of the biggest amount of energy. This is shown were it gives off -2026 kJ/ mol compared to the others where not as much energy is given off.
Method)
Equipment List)
? 5 Fuel Burners containing the different named Alcohols.
? 1 Boiling Tube.
? 1 Thermometer.
? 1 Clamp and Stand.
? 1 Measuring Cylinder.
? 1 Electronic Weighing Scales.
? 450cm3 of Water.
Safety)
? The alcohols we are using are all flammable and so take great care when carrying them around. Make sure any spills of alcohol are cleaned up quickly.
? Make sure you wear goggles at all times, as there is a naked flame being used and an alcohol is being burned so goggles are essential.
? Make sure that when carrying the burner you do so from the bottom where the temperature is low and so there is no risk of dropping the burner.
? Make sure care is taken when carrying the boiling tube as it glass and can be very dangerous.
Fair Testing)
There are several variables in this test. These are as follows:
Changing Variable)
The one changing variable in this experiment is the fuel, or the carbon number. We need to change this, as it is the effector we are looking at and so therefore we need to obtain differing results by changing this.
Measured Variable)
The one thing in this experiment is the amount of energy given off by each fuel. This will be carried out using a thermometer placed in water above the fuel, so therefore it will measure the amount of energy given off as it will record the temperature increase or decrease in the water.
Constant Variable)
There are several variables that we will be keeping constant in this experiment. Here they are:
? Distance from tip of flame to bottom of boiling tube. This is essential that we keep this constant, as this will dictate the amount of energy given off to the boiling tube. If we did not keep this constant then some of our experiments would be false as we would not have made sure that every time we carried out the experiment the same amount of energy that was possible for each fuel was given off.
? Amount of Water. This is also essential because if we differed the amount of water throughout the experiment we would not receive true values as some of the fuels would have to heat more water than others, therefore there would be a greater amount of particles to heat up and so the water would not heat up as much.
? Length of wick. This is very essential as the greater the wick, the more energy could be given out to the water, so we decided on a fixed length of 1cm. This would ensure that the same size flame would be present in all the experiments on every one of the burners.
Set up the equipment mentioned above as follows:
Plan:
? Measure out 30cm3 of water using the measuring cylinder into the boiling tube.
? Place the boiling tube in the clamp and stand and situate the burner directly underneath.
? Then measure the distance between the wick and the bottom of the boiling tube. Make sure it is exactly 2cm.
? Take the weight of the burner using an electronic weighing scales. Make sure it is noted.
? Light the wick underneath the boiling tube and leave until the water has raised in temperature by 200C.
? Reweigh the burner and note down the new weight.
Repeat this experiment three times for each fuel burner.
See results table on extra sheet for results of the experiment.
Here are my practical ? H:
To work out the practical ? Hs for each fuel I need the molar masses of each one.
The molar masses for each fuel are as follows:
Methanol- 32g/mol
Ethanol- 46g/mol
Propan-1-ol- 60g/mol
Propan-2-ol- 60g/mol
Butan-1-ol- 74g/mol
Methanol- 2520
0.443 =5.688487585
=5.69
32 x 5.689
=182.048
=182.05
? H Methanol= -182.05 kJ/mol *
Ethanol- 2520
0.297 =8.484848485
=8.48
46 x 8.48
=390.08
? H Ethanol= -390.08 kJ/mol *
Propan-1-ol- 2520
0.257 =9.805447471
=9.81
60 x 9.81
=588.60
? H Propan-1-ol= -588.60kJ/mol *
Propan-2-ol- 2520
0.323 =7.801857585
=7.80
60 x 7.80
=468.00
? H Propan-2-ol= -468.00kJ/mol *
Butan-1-ol- 2520
0.173 =14.56647399
=14.57
74 x 14.57
=1078.18
? H Butan-1-ol= -1078.18kJ/mol *
Note)
* The minus means the reaction was exothermic *.
Fuel
How much energy was given off
Methanol
-182.05 kJ/ mol
Ethanol
-390.08 kJ/ mol
Propan-1-ol
-588.60 kJ/ mol
Propan-2-ol
-468.00 kJ/ mol
Butan-1-ol
-1078.18 kJ/ mol
Conclusion)
From my results I can see that my practical ? Hs were different to my theoretical ? H. I believe this is because of the energy lost as heat and light to the surroundings, so therefore not all of the water could be heated with the same amount of energy that was given off by the fuel. To some extent though, the ? Hs are similar in that they rise with every fuel.
Also I believe that the wicks on each on the fuels were not exactly the same for each fuel burner. I believe that this could affect the energy given off by each fuel burner.
My prediction was correct in that each fuel did give off energy, and that the more larger the alcohol, the greater the amount of energy that was given off. I was also correct in saying that the more complex the fuel, and the more components in it, the greater the amount of energy that will be given off. This is evident from my results were it shows that the largest of the alcohols, Butan-1-ol, gave off the most energy, 1078.18 kJ/ mol.
I believed this because of the fact that it takes more energy to break all the bonds with the bigger alcohols between atoms but also a greater amount is given off when the new bonds are formed, and so, the greater the size of the alcohol, the greater the amount of energy given off when the new bonds are formed.
The relationship between the size of the compound of the fuel and the amount of energy given off when new bonds form is that they are directly proportional to each other. This is clearly evident from my results, where it shows the following:
Greatest Fuel)
1) Butan-1-ol, giving off 1078.18 kJ/ mol
2) Propan-1-ol, giving off 588.60 kJ/ mol
3) Propan-2-ol, giving off 468.00 kJ/ mol
4) Ethanol, giving off 390.08 kJ/ mol
5) Methanol, giving off 182.05 kJ/ mol
Evaluation)
I believe that my experiment was quite successful in some ways as I proved that each fuel did give off energy, and that the more complex the fuel, the greater the amount of energy that was given off. This shows that my prediction turned out to be correct.
As you can see from my results, I had 1 set of anomalous results, from Propan-2-ol. They do not fit the pattern set by the other fuels. I believe that this was due to the wick on the Propan-2-ol fuel burner. This was the only wick throughout the experiment we had trouble with. The wick constantly burned down so that a small flame was being produced and although it was constantly being raised I believe this to be the reason for our anomalous result for Propan-2-ol as the small flame would have meant that not as much energy was being released from the fuel.
I believe that in this investigation I have been quite accurate, as I have been measuring to 3 decimal places in the Average Mass Change in the results table. Also, whilst working out the ? Hs I have taken the working throughout to equation without rounding any numbers until the final answer.
If I had to repeat this experiment again, I would have to try to find a solution to the fuel burners wicks. This is because I had trouble with them, especially with the Propan-2-ol fuel burner's wick. This was evident from my results. I would also try to think of a way to overcome the problem of the great amounts of energy loss to the surroundings as this affected our results intensely. These changes would, in my opinion give us more satisfactory results and practical ? Hs that were a lot closer to the theoretical ? Hs.
I believe that realistically this was not a real fair test and this was due to all of the surroundings and the amount of heat lost to them. The flame of each burner was a naked flame and it was in open air, which would and did affect the experiment greatly.
Extra Information)
I could get extra information for this experiment by carrying out more preliminary tests or looking up from books and encyclopaedias. Another major source of information that could be useful in my investigation is the Internet. This extra work could help me to predict much more precisely and of greater accuracy. It would also give me more background information and hopefully help me to understand and grasp the concepts of fuels, combustion and other related topics.
I believe that a major aspect of receiving greater information of 'The Combustion of Fuels' would be to take this experiment to another step and use a greater amount of fuels, for example:
? Pentanol
? Hexanol
? Heptanol
Etc.
However, even though I would find new topics and related subjects to my investigation, I would also find a great amount of the same as to what I already have obtained as many sources contain the same work.
________________________________________
Butan-1-ol
Propan-2-ol
Propan-1-ol
Ethanol
Methanol
Fuel
92.55 192.38 192.21
97.91 198.88 198.30
34.84 134.57 134.29
89.81 189.52 189.17
45.71 145.25 140.03
) 2) 3)
Mass Before (g)
92.38 192.21 192.03
97.56 198.57 197.98
34.59 134.31 134.03
89.54 189.20 188.87
45.28 144.83 139.55
) 2) 3)
Mass After (g)
0.17 0.17 0.18
0.34 0.31 0.32
0.25 0.26 0.26
0.27 0.32 0.30
0.43 0.42 0.48
) 2) 3)
Mass Change (g)
0.17 g
0.32 g
0.26 g
0.30 g
0.44 g
Average Mass Change (g)
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