What is a bomb calorimeter?

A bomb calorimeter is a constant-volume calorimeter used to measure the heat of combustion of a substance. The sample is burned in excess oxygen inside a sealed steel "bomb," and the heat released raises the temperature of surrounding water. Because volume is constant, the measured quantity is the internal energy of combustion (ΔUcomb), not ΔHcomb directly — though for most solids and liquids the difference is small.

How is heat of combustion calculated?

Heat released: q = Ccal × ΔT, where Ccal is the calorimeter heat capacity (kJ/°C) and ΔT is the temperature rise. Calorific value (kJ/g) = q ÷ mass. Molar heat of combustion (kJ/mol) = (q ÷ mass) × molar mass. The sign convention here uses a positive ΔT → exothermic reaction → negative ΔHcomb (heat released by the substance).

What is a typical heat capacity for a bomb calorimeter?

Commercial bomb calorimeters have heat capacities typically ranging from 8 to 12 kJ/°C. The exact value (Ccal) is determined by calibration with a standard substance such as benzoic acid (ΔHcomb = −26.4 kJ/g).

Why is the result negative?

Combustion is exothermic — energy flows from the sample to the surroundings. By thermodynamic convention, ΔHcomb is negative for exothermic reactions. The calculator displays the magnitude of heat released and also shows the signed value (−) to follow IUPAC convention.

What is the difference between calorific value and heat of combustion?

Calorific value (also called heating value or specific energy) is the heat released per gram (kJ/g). Heat of combustion (ΔHcomb) is the heat released per mole (kJ/mol). Both describe the same reaction; the difference is only the unit basis.

Bomb Calorimetry Calculator

Enter temperature rise, heat capacity, and sample mass to calculate heat of combustion and calorific value from bomb calorimeter data.

Calorimeter Data

Temperature Rise (ΔT)

°C

Measured temperature increase (T_final − T_initial)

Calorimeter Heat Capacity (C_cal)

kJ/°C

Determined by calibration (commonly 8–12 kJ/°C)

Sample Mass

Mass of substance burned in the bomb

Molar Mass (optional)

g/mol

Required to calculate ΔH_comb in kJ/mol

Formula

q = C_cal × ΔT

Calorific value = q / mass

ΔH_comb = −(q / mass) × M

q = heat released (kJ) | M = molar mass (g/mol)

Enter calorimeter data and click Calculate

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Summary

This bomb calorimetry calculator uses the relationship q = Ccal × ΔT to compute the heat released when a sample is burned in a constant-volume calorimeter. Enter the observed temperature rise, the calorimeter heat capacity, and the sample mass to get the calorific value in kJ/g. Add the molar mass of the substance to also obtain the standard molar heat of combustion (ΔHcomb) in kJ/mol, consistent with IUPAC sign conventions for exothermic processes.

How it works

Enter the temperature rise (ΔT) observed in the calorimeter after combustion.
Enter the heat capacity of the calorimeter (Ccal) in kJ/°C.
Enter the mass of the sample burned in grams.
Optionally enter the molar mass of the substance to get ΔHcomb in kJ/mol.
The calculator applies q = Ccal × ΔT to find the heat released.
Results show calorific value (kJ/g) and molar heat of combustion (kJ/mol) if molar mass is provided.

Use cases

Determine the calorific value of a fuel sample in the lab.
Calculate standard enthalpy of combustion for organic compounds.
Validate bomb calorimeter experiment results in undergraduate chemistry.
Compare energy content of different fuels or food samples.
Cross-check measured ΔHcomb against literature values.
Support thermochemistry coursework and laboratory reports.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu