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The heat of combustion, ΔHcomb, is defined as the amount of heat released by the complete combustion of one mole of a substance. In this experiment, we aim to calculate the heat of combustion of candle wax using calorimetry.
The combustion of candle wax can be represented by the equation:
C32H66 + 97O2 → 66H2O + 64CO2
ΔHcomb = -3086.72 kJ
We conducted the experiment using the following apparatus:
| Hazard | Risk | Precaution |
|---|---|---|
| Open flames | Burns to the skin, hair/clothing catching alight | Long hair should be tied back. Loose clothing or accessories should be removed or secured. |
| Hot water/surfaces | Burns to skin | Allow objects to cool down before touching them. |
| Hot wax | Burns to skin | Do not touch melted wax until it has fully hardened and cooled down. |
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Position the candle 2 cm below the top of the tripod.
| Trial | Mass of Candle (g) | Mass of Empty Can (g) | Mass of Can and Water (g) | Initial Temperature of Water (°C) | Final Temperature of Water (°C) | Final Mass of Candle (g) | Heat Absorbed by Water (kJ) |
|---|---|---|---|---|---|---|---|
| 1 | 23.08 | 12.60 | 59.87 | 22 | 57 | 21.9 | 6.92 |
| 2 | 21.9 | 11.67 | 57.60 | 23 | 56 | 20.84 | 6.34 |
| 3 | 20.84 | 11.70 | 59.71 | 23 | 53 | 19.75 | 6.02 |
| 4 | 19.75 | 11.74 | 58.66 | 27 | 72 | 18.43 | 8.83 |
| 5 | 27.66 | 12.66 | 52.40 | 27 | 73 | 26.05 | 7.64 |
Q = MC∆T
Q (kJ) = (Mass of Water (g) * Specific Heat (4.18 J/g°C) * Change in Temperature (°C)) / 1000
Average Heat Absorbed by Water = 7.15 kJ (2 significant figures)
N (moles) = Mass of Candle Lost (g) / Molecular Weight (g/mol)
N = 0.00232 moles
Q1/Q2 = 7.15 kJ / 0.00232 moles = 3086.72 kJ/mol
Compared to the accepted value of approximately 13,000 kJ/mol, this represents a percentage error of 76.26%.
A candle is generally composed of a wax base but can also be made from microcrystalline wax, beeswax, gel (a mixture of polymer and mineral oil), or some plant waxes (generally palm, carnauba, bayberry, or soybean wax) with a wick commonly made out of braided cotton.
All waxes are hydrocarbons which means that it is a compound of hydrogen and carbon. A candle burns by the base of the flame burning on the wick melting the surrounding wax which then travels back up the wick via capillary action. The heat vaporizes the wax and transforms it into a hot liquid wax which then begins to break down the hydrocarbons within it. The molecules drawn into the flame then react with the oxygen in the air to create water vapor, heat, light, and carbon dioxide. This process then continues until there is no longer any wax/fuel to consume or until the flame is extinguished by an external source. The energy produced in the burning of a candle is heat and light energy.
Calorimetry measures the heat released or absorbed during a chemical reaction. To measure these heat changes, a calorimeter measures the mass of the liquid and the change in temperature to find the amount of energy gained or lost within the liquid. [Insert labeled diagram here.]
The calorimetry equation is Q = MC∆T, where Q is measured in joules (J), M is in grams (g), C is in degrees Celsius (°C), and ∆T is in degrees Celsius (°C).
A mole is the standard scientific unit used to measure large quantities of very small entities such as atoms and molecules. It is defined as approximately 6.02214076 × 10^23 particles and is known as Avogadro’s number.
An exothermic reaction is a reaction that releases heat, light, or sound and may occur spontaneously. Combustion is classified as an exothermic reaction because it results in the release of energy in the form of heat and light. The combustion of hydrocarbons with oxygen produces carbon dioxide and water, releasing energy in the form of light and heat.
Water has a high specific heat capacity, meaning it is resistant to temperature changes and can maintain a stable temperature for a longer duration when heated by an external source, such as a flame. This property allows other substances inside the calorimeter to absorb heat effectively. Additionally, water remains in liquid form over a wide temperature range, allowing for accurate temperature measurements with a thermometer. Water is readily available and cost-effective, making it an ideal choice for calorimetry experiments.
The first law of thermodynamics states that energy cannot be created or destroyed but can be converted from one form to another through interactions of work, heat, and internal energy. The formula representing this law is ΔU = q + w.
Applying the first law of thermodynamics to a calorimetry experiment suggests that the energy produced by the candle (q) will be equal to the energy gained by the water in the calorimeter. However, factors like heat efficiency may cause some energy loss due to external factors. In ideal conditions, the energy gained by the water should equal the energy produced by the combustion of the candle.
| Chemical Formula | Heat of Combustion (kJ/mol) |
|---|---|
| Methane (CH4) | -890 |
| Propane (C3H8) | -2220 |
| Butane (C4H10) | -2874 |
| Octane (C8H18) | -5460 |
In conclusion, the heat of combustion for candle wax, as calculated in this experiment, was found to be 3086.72 kJ/mol, significantly lower than the accepted value of approximately 13,000 kJ/mol. This discrepancy resulted in a percentage error of 76.26%. The sources of error include systematic errors related to flame placement and random errors due to variations in environmental conditions. To enhance the validity and accuracy of the results, experiments should be conducted under controlled environmental conditions and with improved flame placement accuracy.
Diesel engines are often used in large trucks because diesel fuel produces more heat per liter than petrol (gasoline). This difference in heat production can be attributed to the nature of the molecules in diesel fuel compared to petrol, specifically octane (C8H18).
Diesel fuel molecules, such as those in C12H26, have a higher molecular weight and contain more carbon atoms than octane. Diesel molecules are larger and have a more complex structure, which allows them to store and release more energy during combustion. When these larger diesel molecules undergo combustion, they break down into smaller molecules, releasing a significant amount of heat energy.
In contrast, octane, a component of petrol, has a smaller molecular weight and fewer carbon atoms per molecule. This results in less energy being released during combustion compared to diesel. As a result, diesel engines are more fuel-efficient and produce higher torque due to the greater heat energy generated per liter of fuel.
While the experiment provided valuable insights into the heat of combustion for candle wax, several improvements can enhance the validity and accuracy of future experiments:
In this calorimetry experiment, we aimed to calculate the heat of combustion for candle wax. While the results yielded a calculated value significantly lower than the accepted value, valuable insights were gained into the principles of calorimetry, combustion, and the factors influencing experimental accuracy.
By addressing the sources of error and implementing the suggested improvements in future experiments, we can work towards obtaining more precise and reliable measurements of the heat of combustion for candle wax. This knowledge contributes to a better understanding of energy transfer in chemical reactions and its practical applications in various fields.
Calorimetry Experiment: Candle Wax Combustion Analysis. (2024, Jan 12). Retrieved from https://studymoose.com/document/calorimetry-experiment-candle-wax-combustion-analysis
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