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Laboratory Report
Experiment 1: Bomb Calorimetry
Pre-lab preparation (complete before attending the laboratory).
Watch the Experiment 1 video on Canvas before completing this Pre-lab.
PL 1. Describe bomb calorimetry and the objectives of this experiment (approximately ½ page) (1 mark)
Bomb calorimetry is a process for measuring combustion. The procedure is carried out in a bomb calorimeter, which is tightly controlled chamber where the required amount of sample burns.Oxygen gas fills the bomb and once this is done it is placed in a particular fixed volume ofwater. On ignition, the sample keeps on burning until it gets completely consumed heatgenerated increases the water temperature. The heat released by combustion being used toheat up water, change in water’s temperature can be taken as an index of how much heat wasinvolved in the combustion process.
The main parts of a bomb calorimeter are:The Bomb: It refers to an air-tight container that surrounds both oxygen and the sampledmaterial.A means of firing: A fuse wire normally When one talks about ignitors with fuses, they’remostly referring to those with fuse wire as their anode element.
A jacket containing water: Placed around the bomb during combustion helps to take-up anyheat generated.
A device for measuring temperature: This may consist of accurate thermometer orthermocouple taking differential readings of temperatures
It is required that the heat released during combustion be applied to heating water and bomb calorimeter in line with the first law thermodynamics principle. The total heat capacity of a system should be given or measured using a substance with known heat of combustion such as benzoic acid for instance so as to calculate the sensible heat ‘O’.
PL 2. Briefly define the following terms and explain their relevance to this experiment: (1.5 marks)
Internal energy:
Definition: The total energy contained within a system, including all the kinetic and potential energy of its molecules.
Relevance: In this experiment, the internal energy change (ΔU) during combustion tells us how much energy is released as heat when naphthalene burns in the bomb calorimeter.
State function:
Definition: A property that depends only on the current state of the system, not on how the system got there.
Relevance: Internal energy and enthalpy are state functions, meaning the energy change measured during the experiment is the same regardless of the path taken to reach that state.
Heat capacity:
Definition: The amount of heat needed to raise the temperature of a substance by one degree Celsius (or one Kelvin).
Relevance: To calculate the heat released during combustion, we need to know the heat capacity of the calorimeter. This tells us how much the temperature of the calorimeter's water will rise for a given amount of heat.
Enthalpy:
Definition: The total heat content of a system, combining internal energy with the energy needed to displace its surroundings (pressure-volume work).
Relevance: While the experiment measures energy changes at constant volume, enthalpy is useful for understanding heat changes at constant pressure, which is common in many reactions.
Standard state:
Definition: The most stable form. of a substance at 1 atmosphere of pressure and a specified temperature, typically 25°C (298.15 K).
Relevance: Standard state conditions provide a baseline for comparing the heat of combustion and other thermodynamic properties across different substances and reactions.
Hess’s law:
Definition: The total enthalpy change of a reaction is the same, no matter how many steps the reaction takes.
Relevance: Hess’s law helps us calculate the heat of combustion by combining known enthalpies of different steps, allowing us to determine the overall energy change indirectly.
PL 3. Complete the below table: (0.5 marks)
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Standard state at room temperature (298 K) and 1 atm pressure. |
Water |
Liquid |
Benzene |
Liquid |
Benzoic acid |
Solid |
Carbon dioxide |
Gas |
Naphthalene |
Solid |
PL 4. Summarise any safety information and precautions for this laboratory. (1 mark)
Always wear personal protective equipment, including lab coats, safety goggles, and gloves. Keep flammable materials away from the combustion area and ensure a fire extinguisher is accessible. Handle the bomb calorimeter carefully, securing all fittings and valves to prevent leaks and sudden pressure releases. Tighten the bomb's retaining ring securely and have it checked by a supervisor. Ensure the fuse wire is correctly positioned to avoid misfires. During the experiment, allow the calorimeter to reach thermal equilibrium before and after ignition for accurate measurements. If the bomb fails to ignite, seek guidance before attempting re-ignition. After the experiment, release pressure slowly and inspect for incomplete combustion, which requires repetition. Clean the bomb with deionized water, handling parts carefully to avoid damage. Handle benzoic acid and naphthalene with care, and dispose of waste according to guidelines.
Laboratory report.
Calculations should be carried out using Excel, but you must provide one fully worked example for each of the calculations. Uncertainties are not required for this experiment. Do not forget to use units for your answer and during your calculations.
Experimental procedure.
Write an experimental procedure for this experiment (see laboratory manual for guidance on how to write this). (2 marks)
Results and Discussion.
1. Complete the below table of experimental results. Add additional rows if necessary. (0.5 marks)
Sample |
Mass (g) |
Length of initial fuse wire (cm) |
Lengths of residual fuse wire (cm) |
Length of fuse wire burned (cm) |
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Benzoic acid run 1 |
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Benzoic acid run 2 |
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Naphthalene run 1 |
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Naphthalene run 2 |
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2. Calculation of ΔT for each calorimetry experiment run: (see section 2.2)
2 a) Plot temperature vs. time. (see Laboratory Manual section 6.2 for how to plot your data) (1.5 marks)
2 b) Identify on your plot:
· a (time of firing)
· b (time when temperature reaches 63.2% of total rise)
· c (time at beginning of period when the rate of temperature change is linear)
(1 mark)
2 c) Fit linear lines to your data and perform. regression to determine the parameters r1 (the rate of change of temperature during the 5 minutes before firing) and r2 (the rate of change of temperature during the 5 minutes after time c). Display these values on your plots. (see Laboratory Manual section 6.5 for how to fit separate linear regression models for different sections of your data) (1.5 marks)
Benzoic acid run 1:
Benzoic acid run 2:
Naphthalene run 1:
Naphthalene run 2:
2 d) Calculate ΔT. Use equation (1). (1 mark)
Complete the table below (do not forget units):
Run |
a |
b |
c |
r1 |
r2 |
ΔT |
Benzoic acid run 1 |
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Benzoic acid run 2 |
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Naphthalene run 1 |
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Napthalene run 2 |
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3. Calculation of C.
3 a) Calculate the energy liberated (q) by the combustion of the mass of benzoic acid used for each run. Use equation (2). (0.5 marks)
Benzoic acid run 1:
Benzoic acid run 2:
3 b) Determine the heat capacity (C) of the water. Use equation (3). (0.5 marks)
Benzoic acid run 1:
Benzoic acid run 2:
3 c) Calculate the average value of C. (0.5 marks)
4. Calculation of thermodynamic properties of naphthalene.
4 a) Use your calculated average C to determine the energy liberated (q) by burning each sample of naphthalene. Use equation (4). (0.5 marks)
Naphthalene run 1:
Naphthalene run 2:
4 b) Calculate the heat of combustion (ΔU in J g-1) for each naphthalene sample. Use equation (5). (1 mark)
Naphthalene run 1:
Naphthalene run 2:
4 c) Calculate the molar heat of combustion (ΔU in J mol-1) for each sample of naphthalene. (0.5 marks)
Naphthalene run 1:
Naphthalene run 2:
4 d) Calculate the average molar heat of combustion for your naphthalene samples. Use this value for your further calculations. (0.5 marks)
4 e) Calculate the enthalpy of combustion (ΔcH, in kJ mol-1) for naphthalene. See section 2.4. (1 mark)
4 f) Calculate the enthalpy of formation (ΔfH, in kJ mol-1) for naphthalene. See section 2.5. (1.5 mark)
4 g) Calculate the delocalisation energy (ΔdelocE, in kJ mol-1) for naphthalene. See section 2.6. (2 mark)
5. Comparison to Literature.
Compare your experimentally determined molar heat of combustion and enthalpy of formation values (for naphthalene) with literature values. Provide experimental reasons for the discrepancy between your values and literature. (2 marks)