Calorimetry Calculator
Find the heat absorbed by the water in a calorimeter — q = m c ΔT — and the enthalpy change per mole of the reactant, from a temperature rise.
From a temperature rise in the cup to kJ per mole of reaction.
How the calorimetry calculator works
In a simple calorimeter the heat released by a reaction warms the water: q = mass × specific heat × temperature change, with water's specific heat 4.18 J/g·°C. Divide by the moles of the reactant that reacted for ΔH per mole; the sign is negative for an exothermic reaction (the water warmed up).
Coffee-cup calorimeters lose heat to the surroundings, so results are usually a little below the literature value.
Formula: q = m c ΔT · ΔH = −q ÷ n
Worked examples
| Inputs | Heat absorbed by the water | Note |
|---|---|---|
| 100 g water warms 6.8 °C; 0.05 mol reacted | 2,842.4 J | 2,842 J → −56.8 kJ/mol (neutralisation) |
| 50 g water cools 3.0 °C; 0.02 mol dissolved | -627 J | endothermic: +31 kJ/mol |
| 250 g water warms 12 °C | 12,540 J | 12.5 kJ |
FAQFrequently asked questions
Why is ΔH negative when the water warms?
Convention: ΔH describes the reaction. Heat leaving the reaction into the water is a loss for the system, so exothermic ΔH is negative.
What about the heat absorbed by the cup?
A polystyrene cup absorbs little; a metal or glass calorimeter needs its heat capacity added (q = C_cal × ΔT). Enter a higher effective specific heat in Detailed mode if you have calibrated it.
What is the specific heat of water?
4.18 J per gram per degree — one of the highest of common substances, which is why water makes a good calorimeter fluid.
My value is lower than the textbook — why?
Heat loss to the air and the cup, and the reaction not going to completion. Insulating the cup and taking the maximum temperature quickly reduce the gap.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.