Bomb Calorimeter Calculator
Heat of combustion from a temperature rise.
Work out Bomb Calorimeter. Heat of combustion from a temperature rise. Kelvin conversion handled for you.
Measured by burning a standard such as benzoic acid, not calculated. Includes the bomb, water and hardware.
Leave at zero to skip the per-mole figure.
Heat released
25.2 kJ
1,260 kJ per mole of sample
A bomb calorimeter runs at constant volume, so it measures ΔU rather than ΔH. The two are equal when the reaction produces no net change in moles of gas, and otherwise differ by ΔnRT — usually only a few kJ, but a real difference. The calorimeter constant has to be measured rather than worked out, because it lumps together the water, the steel bomb, the stirrer and the thermometer. Benzoic acid at 26.43 kJ/g is the standard used to determine it. This is the instrument behind food Calorie labels, though the figure is then adjusted downwards, because a body does not extract all the energy that a bomb does.
How the Bomb Calorimeter Calculator works
Enter the calorimeter constant and the temperature rise to get the heat released, then optionally per mole and per gram of sample. Constant volume means this measures internal energy rather than enthalpy, which the page explains where it matters.
Also known as: calorimeter constant calculator · heat of combustion calculator · constant volume calorimetry calculator · q = c delta t calculator
Frequently asked questions
How does a bomb calorimeter work?
A sample is burned in pure oxygen inside a sealed steel vessel, and the temperature rise of the surrounding water is measured. q = C·ΔT, where C is the calorimeter constant.
Why is the calorimeter constant measured rather than calculated?
Because it lumps together the water, the steel bomb, the stirrer and the thermometer, all of which absorb heat. It is determined by burning a standard of known energy, usually benzoic acid at 26.43 kJ/g.
Does this give ΔH or ΔU?
ΔU, because the volume is fixed and no expansion work is done. They are equal when the reaction produces no net change in moles of gas, and otherwise differ by ΔnRT — usually a few kJ.
Is this how food Calories are measured?
Historically yes, and the numbers are still calibrated against it. Modern labels use Atwater factors that adjust the raw figure downwards, because a body does not extract all the energy a bomb does — dietary fibre being the clearest example.
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