Thermochemistry
Enthalpy Calculator
Find ΔH by calorimetry, Hess's law, phase change, or bond enthalpy — and see if a reaction is exo- or endothermic.
Method
Mass
g
Substance
J/g·°C
Temperature Change (ΔT)
°C
Positive = warmed up (absorbed heat); negative = cooled down (released heat)
Moles (optional)
mol
Set >0 to also get molar ΔH (kJ/mol)
📏 Compare Against
Of Reference
Magnitude 0%
Magnitude 0%
ΔH (Enthalpy Change)
0 kJ
—
Heat (q)
0 J
Molar ΔH
N/A
Method
Calorimetry
Reference Comparison
0%
📊 Calculation Breakdown
| Quantity | Value | Note |
|---|
Governing equations
q=mcΔT | ΔH_rxn=ΣΔHf(products)−ΣΔHf(reactants) | q=nΔH | ΔH_rxn=ΣE(broken)−ΣE(formed)
- Calorimetry: q = mass × specific heat × ΔT — heat absorbed (+) or released (−) by a substance itself
- Hess's Law: ΔH_rxn = Σ(coeff. × ΔHf products) − Σ(coeff. × ΔHf reactants), using standard enthalpies of formation
- Phase Change: q = moles × ΔH per mole (fusion, vaporization, or sublimation)
- Bond Enthalpy: ΔH_rxn = Σ(energy to break reactant bonds) − Σ(energy released forming product bonds)
- Negative ΔH → exothermic (releases heat to surroundings); positive ΔH → endothermic (absorbs heat from surroundings)
⚠️ Bond enthalpies are averages across many compounds and give only an approximate ΔH — Hess's law with tabulated ΔHf values is generally more accurate. All methods here assume standard conditions and ignore entropy, so they say nothing about whether a reaction is spontaneous.