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LIVE LAB 23 • THERMOCHEMISTRY
Explore combustion in a 3D calorimeter, compare sample and water masses, and solve 20 questions with worked solutions.
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COMPLETE CONCEPT GUIDE
A bomb calorimeter uses a temperature change to determine the energy released by combustion in a rigid vessel. Explore the labelled 3D apparatus, vary the sample and water masses, follow the temperature graph, and connect each run with thermochemical calculations and 20 worked practice questions.
The reaction occurs in a rigid vessel, so its volume remains constant. With pressure–volume work absent and other work neglected, the reaction heat at constant volume equals its internal-energy change: qᵥ = ΔU. It does not automatically equal the enthalpy change.
Combustion transfers energy from the sample to the surrounding water and hardware. In the ideal insulated model, qᵣₓₙ = −q(calorimeter). A positive water-temperature rise therefore corresponds to negative reaction heat. Keep the reaction and calorimeter signs distinct.
This lab separates water from hardware: q(calorimeter) = (m c + Cₕ)ΔT, where m is water mass, c its specific heat capacity and Cₕ the hardware heat capacity. If a calibrated total heat capacity already includes water, use q(calorimeter) = C(total)ΔT without adding water again.
Keep the sample material fixed and increase its mass to compare the energy supplied. Then keep the sample fixed and increase water mass. The same released energy produces a smaller temperature rise when the total receiving heat capacity is larger.
A standard with known combustion energy can establish the calorimeter’s total heat capacity from energy absorbed divided by temperature rise. Divide the reaction energy by the amount burned to obtain molar internal-energy change; check units and retain the negative combustion sign.
For ideal-gas contributions compared at the same temperature, ΔH = ΔU + ΔnᵍRT. Here Δnᵍ counts gaseous products minus gaseous reactants from the balanced equation. Use kelvin and consistent energy units. Liquid water is not counted as a gas.
The model assumes a precharged oxygen chamber, complete combustion, perfect insulation, and no ignition-wire or acid corrections. Its results illustrate the energy balance; real measurements require calibration and appropriate experimental corrections.
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STUDENT DISCUSSION
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BOMB CALORIMETER FAQ
It measures combustion energy from the temperature increase of a calibrated surrounding assembly. The sample burns inside a strong, rigid vessel rather than directly in the surrounding water.
Its constant-volume reaction heat corresponds to ΔU when other work is neglected. ΔH requires any relevant gas-mole correction; the two quantities should not be treated as universally identical.
For the same sample energy, more water increases the total heat capacity receiving that energy. The equilibrium temperature rise becomes smaller, even though the same total energy is transferred.
Yes. This simulation includes water plus hardware. In other problems, check whether a stated calorimeter constant already describes the whole assembly, so that water is not counted twice.
The rigid bomb operates at constant volume. A coffee-cup calorimeter usually operates near constant external pressure; under the corresponding assumptions its reaction heat measures enthalpy change.
Choose benzoic acid, sucrose, cellulose or vegetable oil; vary sample mass, water mass and initial temperature; rotate or open the apparatus; follow the graph; and practise 20 questions with worked solutions.
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