Parr-Type Plain Oxygen Combustion Bomb (350 mL)
A heavy-walled forged stainless steel vessel with threaded screw cap and sealing O-ring designed to safely withstand internal explosion pressures up to 300 atm during rapid oxygen combustion.
Chemistry / Bomb Calorimetry of Benzoic Acid
FREE TO EXPLORELABORATORY 13 · NATURAL SCIENCES
Determination of the Heat of Combustion of Benzoic Acid via Constant-Volume Oxygen Bomb Calorimetry
Determine the standard molar internal energy of combustion (ΔU_comb°) and molar enthalpy of combustion (ΔH_comb°) of primary standard benzoic acid in a constant-volume oxygen bomb calorimeter, evaluating fuse wire and nitric acid thermochemical corrections, and extracting the combustion energy using ordinary least-squares linear regression. Explore interactive analytical gravimetry, Class A volumetric glassware and density determination.
MEASURE · CALIBRATE · ANALYSE
Your virtual chemistry laboratory.
CORRECTED ADIABATIC TEMPERATURE RISE ΔT—
MEASUREMENT STATUS
Ready to dispense 1.0 g of liquid.
Adjust pellet mass V, then weigh the dispensed aliquot.
Mass observations are determined by the high-precision thermodynamic equation of state for pure liquid water. Readings reflect thermal equilibrium and analytical balance force restoration.
Physical chemistry assumptions and metrological limits
The measurement assumes ideal gas behavior for oxygen and carbon dioxide at high dilution upon pressure release, complete recovery of latent heat of condensation for water, and zero net heat exchange with the ambient environment outside the Regnault-Pfaundler extrapolation window. Trace secondary oxidation of nitrogen to nitric acid contributes <0.05% of the total energy, which is safely absorbed into the linear regression intercept. The physical simulation model calculates the adiabatic constant-volume temperature rise via ΔT = [ |ΔU_comb| / (M_benzoic · C_cal) ] · m + ΔT₀. Calorimeter parameters: distilled water bucket charge m_water = 2000.0 g (specific heat c_p = 4.184 J/(g·K)), bomb and hardware heat capacity C_bomb = 2132.0 J/K. Total calorimeter system effective heat capacity: C_cal = 2000.0 · 4.184 + 2132.0 = 10500.0 J/K = 10.500 kJ/K. Benzoic acid primary standard molar mass: M = 122.12 g/mol. Accepted standard molar internal energy of combustion: ΔU_comb° = −3227.0 kJ/mol. Theoretical thermometric slope: m_slope = |ΔU_comb| / (M · C_cal) = 3227.0 / (122.12 · 10.500) = 2.51686 °C/g. Across pellet charges m = 0.600 g to 1.600 g, adiabatic temperature rises span ΔT = 1.510 °C to 4.027 °C. Thermodynamic gas mole difference: Δn_gas = 7 CO₂ − 7.5 O₂ = −0.5 mol. Standard molar enthalpy of combustion: ΔH_comb° = ΔU_comb° + Δn_gas · R · T = −3227.0 − 1.24 = −3228.24 kJ/mol. Standard thermochemical corrections: nickel-chromium fuse wire burn energy (q_fuse = 35.0 J) and trace nitric acid formation (q_HNO3 ≈ 15 J) are accounted for; multi-point regression eliminates constant fuse wire offsets into the intercept ΔT₀.
Analytical chemistry apparatus & tools.
Precision Oval Water Jacket Bucket and Impeller Stirrer
Holds exactly 2000.0 ± 0.5 g of distilled water around the submerged bomb, circulated by a continuous-speed motorized impeller (400 rpm) to ensure rapid, uniform thermal equilibration.
High-Pressure Oxygen Gas Tank with Two-Stage Regulator
Charges the sealed bomb chamber to 30.0 atm (3.04 MPa) of research-grade 99.99% pure oxygen gas to ensure instantaneous, 100% complete combustion without carbon monoxide formation.
Calibrated Nickel-Chromium Fuse Wire and Electrical Ignition Box
Delivers a 10 cm loop of certified Ni-Cr fuse wire touching the benzoic acid pellet, pulsed with a 23 V AC discharge to ignite the combustion cleanly with a known, calibrated wire burn heat.
Pellet Press and Stainless Steel Die Set
Compresses loose crystalline benzoic acid powder into a dense, coherent cylindrical pellet that burns steadily without splattering unburned particles out of the crucible.
NIST-Calibrated Digital Thermistor Thermometer (±0.001 °C)
Monitors the water bucket temperature continuously at 2 Hz during the pre-period baseline (5 min), thermal excursion (2 min), and post-period cooling tail (10 min).
FOLLOW THE METHOD
A reason behind every step.
Determine the standard molar internal energy of combustion (ΔU_comb°) and molar enthalpy of combustion (ΔH_comb°) of primary standard benzoic acid in a constant-volume oxygen bomb calorimeter, evaluating fuse wire and nitric acid thermochemical corrections, and extracting the combustion energy using ordinary least-squares linear regression. Suggested independent volumetric settings: 0.6, 0.8, 1.0, 1.2, 1.4, 1.6 g.
01
Pellet Preparation and Analytical Gravimetry
Transfer approximately 1.0 g of pure crystalline benzoic acid into the stainless steel pellet die. Compress with the hand press into a firm, coherent cylindrical pellet. Weigh the pellet on an analytical balance to ±0.0001 g and place it in the combustion crucible.
02
Fuse Wire Installation and Bomb Assembly
Cut exactly 10.0 cm of standard nickel-chromium fuse wire (calibrated heat 9.6 J/cm). Clamp the ends to the two bomb ignition electrodes, forming a loop that rests firmly in light contact with the top of the benzoic acid pellet without touching the crucible walls. Add 1.0 mL distilled water to the bomb base to absorb trace acid gases.
03
Oxygen Purging and Bomb Pressurization
Carefully screw down the bomb locking ring until hand-tight. Attach the oxygen filling tube, purge the bomb headspace for 10 seconds to displace nitrogen, and slowly pressurize the bomb to 30.0 atm (3.04 MPa) pure oxygen. Check for leaks in a water test sink.
04
Water Bucket Loading and Calorimeter Assembly
Tare the clean oval water bucket and add exactly 2000.0 ± 0.5 g of distilled water. Lower the pressurized bomb into the bucket using the lifting handle, ensuring no air bubbles escape from the valves. Place the bucket into the insulated jacket, lower the cover, and engage the stirrer drive belt.
05
Baseline Acquisition and Electrical Firing
Activate the motorized stirrer. Record temperature at 10-second intervals for 5 minutes (300 s) to establish a steady pre-ignition drift rate. Press the firing button to discharge 23 V through the fuse wire. The red indicator lamp flashes, initiating instantaneous deflagration.
06
Thermogram Tracking, Extrapolation and Inspection
Log the rapid thermal excursion and continue recording the post-period cooling decay for 10 minutes (600 s). Extrapolate the pre- and post-period slopes to the 63.2% reaction midpoint to find corrected ΔT. Depressurize the bomb slowly, measure remaining unburned fuse wire, verify complete soot-free combustion, and extract ΔU_comb via regression.
YOUR NOTEBOOK · 0 OBSERVATIONS
Turn measurements into quantitative chemical insight.
Points are your recorded gravimetric observations. The regression line validates the linear mass-volume proportionality and extracts density.
ORDINARY LEAST-SQUARES FIT · m = ρ·V + m₀
ΔT = [|ΔU_comb| / (M_benzoic · C_cal)] · m + ΔT₀ ==> ΔT = 2.517 · m
| # | Benzoic acid pellet mass m (g) (g) | Corrected adiabatic temperature rise ΔT (°C) | Benzoic acid pellet mass m (g) | Corrected temperature rise ΔT (°C) | Remove |
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