Calorimetry Experiment: Candle Wax Combustion Analysis

Introduction

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.

Chemical Reaction

The combustion of candle wax can be represented by the equation:

C₃₂H₆₆ + 97O₂ → 66H₂O + 64CO₂

ΔHcomb = -3086.72 kJ

Methods

Experimental Setup

We conducted the experiment using the following apparatus:

• Candle on a tin/plastic lid
• Aluminium can
• 'Mini' Tripod
• Heat mat
• Thermometer
• Glass stirring rod

Risk Assessment

Hazard	Risk	Precaution
Open flames	Burns to the skin, hair/clothing catching alight	Long hair should be tied back. Don't use plagiarized sources. Get your custom paper on “ Calorimetry Experiment: Candle Wax Combustion Analysis ” Get high-quality paper NEW! smart matching with writer 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.

Procedure

1. Set up the apparatus as shown in the diagram below.
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2. Measure the mass of the candle and lid and record this value in a data table.
3. Place the 'mini' tripod onto a large heat mat. Position the candle 2 cm below the top of the tripod.
4. Measure the mass of an aluminium can and record it.
5. Measure 50 mL of water and place it into the aluminium can. Measure the mass of the can and water.
6. Record the initial temperature of the water.
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7. Light the candle and heat the water for 15 minutes while gently stirring with a glass rod.
8. Blow out the candle and record the final temperature of the water.
9. Measure the final mass of the candle and tin lid assembly.
10. Repeat the experiment for 9 more trials, ensuring the can cools down between trials.

Results

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

Calculations

1. Calculate the heat absorbed by the water for each trial:

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)

2. Calculate the number of moles of candle burned:

N (moles) = Mass of Candle Lost (g) / Molecular Weight (g/mol)

N = 0.00232 moles

3. Calculate the heat of combustion for wax:

Q₁/Q₂ = 7.15 kJ / 0.00232 moles = 3086.72 kJ/mol

Discussion

1. The calculated heat of combustion for candle wax is 3086.72 kJ/mol. Compared to the accepted value of approximately 13,000 kJ/mol, this represents a percentage error of 76.26%.
2. Sources of error include systematic errors in the placement of the flame, and random errors due to variations in room temperature and exposure to wind.
3. To improve reliability, experiments should be conducted on the same day to control for environmental variations.

Research

1. Describe the components of a candle:

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.

2. Explain how a candle burns and the main forms of energy that are produced:

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.

3. Explain how calorimetry is able to measure heat changes during a chemical reaction. Include a labeled diagram in Part 1. of the procedure:

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.]

4. State the calorimetry equation and the units used to measure the heat of combustion:

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).

5. Define the mole as a number used to measure the amount of a substance:

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.

6. What are the criteria used that would classify combustion as an exothermic reaction?

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.

7. Describe why water, with a high specific heat capacity, is used in a calorimetry 'bomb':

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.

First Law of Thermodynamics

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.

8. If this law is applied to a calorimetry experiment, what prediction can we make about the gain in energy of the water in the 'bomb'?

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.

Heats of Combustion

Chemical Formula	Heat of Combustion (kJ/mol)
Methane (CH4)	-890
Propane (C3H8)	-2220
Butane (C4H10)	-2874
Octane (C8H18)	-5460

Conclusion

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 vs Petrol

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.

Improving Experimental Validity

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:

1. Consistent Flame Placement: To address the systematic error related to flame placement, ensure that the distance between the candle flame and the calorimeter remains constant throughout the experiment. This can be achieved by using a fixed apparatus to hold the candle at the desired height.
2. Environmental Control: To minimize the impact of random errors due to variations in room temperature, conduct all trials of the experiment on the same day in a controlled environment with regulated temperature. This will help maintain consistency in the initial conditions of each trial.
3. Wind Shielding: To mitigate the influence of wind on the flame, perform the experiment in a draft-free environment or use a wind shield to protect the flame from external air currents. This will help ensure a more stable heat source for heating the water.

Final Remarks

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.