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Alcohols are considered as a viable alternative fuel for internal combustion engines due to their reduced environmental impact compared to petroleum-based fuels. They produce fewer greenhouse gases and toxic emissions while enhancing overall energy efficiency. Additionally, their high-octane rating, burning velocities, and wider flammability limits contribute to better environmental sustainability.
Combustion is a chemical process in which a substance reacts rapidly with oxygen and releases heat. In this study, we investigate how the length of the carbon chain in alcohols affects their combustion enthalpy.
The alcohols selected, including methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol, all belong to the same homologous series with a common functional group.
The enthalpy of combustion for ethanol, for example, can be represented by the following reaction:
C2H5OH (l) + 3O2 (g) -> 2CO2 (g) + 3H2O (g)
We hypothesize that the longer the carbon chain in the alcohol molecule, the greater its enthalpy of combustion.
Independent Variable: The length of the alcohol's carbon chain.
Dependent Variable: Combustion enthalpy (in kJmol-1).
| Controlled Variable | Control Method | Reason for Control |
|---|---|---|
| The increase of temperature in water | Constant stirring, monitoring temperature change, stopping heating at a 30°C increase | Ensures a constant temperature change in the formula |
| The mass of water in calorimeter | Add 50cm3 into the calorimeter each time | Maintains a constant mass in the formula |
| The ambient temperature and atmospheric pressure | Conduct experiments in the same location, use wind shields to prevent heat loss | Temperature changes affect heat loss; pressure changes affect particle space and reaction rate |
| The distance between the calorimeter and the burner | Keep the position of the calorimeter and spirit burner constant | Changing the distance may affect the rate of temperature change |
| Chemicals | Quantity |
|---|---|
| Methanol | 150 cm3 |
| Ethanol | 150 cm3 |
| 1-Propanol | 150 cm3 |
| 1-Butanol | 150 cm3 |
| 1-Pentanol | 150 cm3 |
| Apparatus | Uncertainty | Quantity |
|---|---|---|
| -10~110°C thermometer | ±0.5°C | 1 |
| Electronic balance | ±0.01g | 1 |
| 100 cm3 Measuring cylinder | ±1.0cm3 | 1 |
| Spirit burner | NA | 1 |
| Wind shields | NA | 1 |
| Clamps and stands | NA | 1 |
| Calorimeter | NA | 1 |
| Equipment or Chemical | Identified Risk | Management Strategy |
|---|---|---|
| Measuring cylinder | Glass cylinder may break during the experiment, causing cuts | Do not heat any liquid in the cylinder.
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Handle broken glass carefully. |
| Heating by spirit burner | Risk of spirit burner bottle collapse and explosion | Close the lid immediately when not in use. Handle the burner with care. |
| Calorimeter | Calorimeter becomes very hot after each trial, risk of burns | Use metal tongs to handle the hot calorimeter when adding or removing water. |
| Disposal of alcohols | Environmental threat due to inhalation and consumption by animals, damage to plants | Do not ingest the chemicals, and store them safely. Dispose of chemicals through specific processes that do not harm the environment. |
Ethical Considerations: This investigation does not involve the use of animal-based products or plant extracts, eliminating ethical concerns.
| Alcohols | Trial | Initial Mass/g (±0.01g) | Final Mass/g (±0.01g) | Initial Temperature/°C (±0.5°C) | Final Temperature/°C (±0.5°C) |
|---|---|---|---|---|---|
| Methanol | 1 | 250.66 | 250.37 | 25.5 | 55.5 |
| Methanol | 2 | 244.92 | 244.64 | 26.0 | 56.0 |
| Methanol | 3 | 233.26 | 232.92 | 27.5 | 57.5 |
| Ethanol | 1 | 231.29 | 231.10 | 28.0 | 58.0 |
| Ethanol | 2 | 229.39 | 229.19 | 28.5 | 58.5 |
| Ethanol | 3 | 225.66 | 225.43 | 29.0 | 59.0 |
| 1-Propanol | 1 | 226.68 | 226.46 | 28.0 | 58.0 |
| 1-Propanol | 2 | 218.94 | 218.73 | 28.0 | 58.0 |
| 1-Propanol | 3 | 217.44 | 217.25 | 28.0 | 58.0 |
| 1-Butanol | 1 | 227.19 | 227.02 | 28.5 | 58.5 |
| 1-Butanol | 2 | 225.61 | 225.40 | 28.0 | 58.0 |
| 1-Butanol | 3 | 223.89 | 223.70 | 29.0 | 59.0 |
| 1-Pentanol | 1 | 230.32 | 230.14 | 27.0 | 27.5 |
| 1-Pentanol | 2 | 228.76 | 228.60 | 27.5 | 57.5 |
| 1-Pentanol | 3 | 227.20 | 227.02 | 28.0 | 58.0 |
| Alcohol | Trial | Mass of Alcohol/g (±0.02g) | Average Mass of Alcohols/g (±0.02g) | Change in Temperature/°C (±1.0°C) | Number of Moles of Alcohol | Enthalpy of Combustion/ kJmol-1 | Average Enthalpy of Combustion/ kJmol-1 |
|---|---|---|---|---|---|---|---|
| Methanol | 1 | 0.29 | 0.303 | 30 | 0.00905 | -692.82 | -667.18 |
| Methanol | 2 | 0.28 | 0.303 | 30 | 0.00874 | -717.69 | |
| Methanol | 3 | 0.34 | 0.303 | 30 | 0.0106 | -591.04 | |
| Ethanol | 1 | 0.19 | 0.207 | 30 | 0.00558 | -1123.65 | -1040.17 |
| Ethanol | 2 | 0.20 | 0.207 | 30 | 0.00599 | -1068.09 | |
| Ethanol | 3 | 0.23 | 0.207 | 30 | 0.00636 | -928.78 | |
| 1-Propanol | 1 | 0.22 | 0.207 | 30 | 0.00366 | -1713.14 | -1830.49 |
| 1-Propanol | 2 | 0.21 | 0.207 | 30 | 0.00349 | -1794.71 | |
| 1-Propanol | 3 | 0.19 | 0.207 | 30 | 0.00316 | -1983.63 | |
| 1-Butanol | 1 | 0.17 | 0.190 | 30 | 0.00229 | -2734.46 | -2527.75 |
| 1-Butanol | 2 | 0.21 | 0.190 | 30 | 0.00272 | -2303.18 | |
| 1-Butanol | 3 | 0.19 | 0.190 | 30 | 0.00246 | -2545.62 | |
| 1-Pentanol | 1 | 0.18 | 0.173 | 30 | 0.00204 | -3071.26 | -3199.23 |
| 1-Pentanol | 2 | 0.16 | 0.173 | 30 | 0.00181 | -3455.16 | |
| 1-Pentanol | 3 | 0.18 | 0.173 | 30 | 0.00204 | -3071.26 |
| Alcohol | Percentage Uncertainty | Absolute Uncertainty |
|---|---|---|
| Methanol | 10.27% | -68.51 |
| Ethanol | 13.33% | -138.65 |
| 1-Propanol | 13.33% | -244.00 |
| 1-Butanol | 14.19% | -358.69 |
| 1-Pentanol | 15.23% | -487.24 |
Percentage Uncertainty = (Absolute Uncertainty / Measured Value) x 100%
The hypothesis that the enthalpy of combustion of alcohols increases as the carbon chain length increases is supported by the results. The negative values of enthalpy of combustion indicate an exothermic process, and the greater the negative value, the greater the combustion enthalpy.
Percentage uncertainty and absolute uncertainty varied for each alcohol, with a trend indicating that longer carbon chains had greater uncertainty. The observed trend can be attributed to the increase in molecular size and intermolecular bond strength with longer carbon chains.
Comparing theoretical and experimental values revealed that experimental values were consistently lower than theoretical values, resulting in percentage errors. The experiment's reliability is supported by the goodness of fit (R2 value) of the trend lines.
Overall, the experiment demonstrated that longer carbon chains in alcohols lead to higher combustion enthalpy, highlighting the potential of longer-chain alcohols as alternative fuels.
The study has several advantages, including its simplicity and ease of replication. However, there are areas for improvement, particularly in minimizing random errors. To enhance the precision and accuracy of the experiment, the following improvements are suggested:
| Random Errors | Effects on Results | Suggested Improvement |
|---|---|---|
| Wind current affects reading of mass | Mass may be less or greater than actual | Switch off fans and air conditioners during measurements and weigh masses when no one is passing through the area. |
| Inconsistent rate of stirring | Faster stirring increases the chances of collisions and shortens the time taken | Utilize a magnetic stirrer to ensure consistent and controlled stirring of the reactants. |
| High instrument errors of 100 cm3 measuring cylinder | The uncertainty of the measuring cylinder can cause variations in the amount of water poured into the calorimeter | Use a micropipette to measure smaller volumes or improve the precision of the measuring instruments. |
| High instrument errors of -10°C | Instrument uncertainty may affect temperature measurements | Calibrate and use more precise thermometers to minimize temperature measurement errors. |
By addressing these sources of random errors, future experiments can achieve both precision and accuracy in measuring combustion enthalpy.
Limitations: The study may have been affected by systematic errors, and certain assumptions may have influenced accuracy, particularly in the case of ethanol. Further investigations into these systematic errors are warranted.
Future Research: Future research could explore the effects of other factors, such as pressure and oxygen concentration, on combustion enthalpy to gain a more comprehensive understanding of alcohol fuels' behavior.
Overall, this study contributes to the understanding of the relationship between carbon chain length and combustion enthalpy in alcohols, which has implications for the development of more sustainable fuel alternatives.
The Effect of Carbon Chain Length on Combustion Enthalpy of Alcohols. (2024, Jan 11). Retrieved from https://studymoose.com/document/the-effect-of-carbon-chain-length-on-combustion-enthalpy-of-alcohols
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