Unit Conversion

Convert numbers between two units quickly and precisely

Molar/Atomic Energy Converter

Unit Conversion

Convert molar energy: hartree, electronvolt, and kJ/mol

In quantum chemistry and spectroscopy, energy is often stated per particle – for example in hartree (Eh, the atomic unit of energy), rydberg (Ry), or electronvolt (eV). In classical thermodynamics and for reaction energies, calculations are usually done per mole, in kilojoule per mole (kJ/mol) or kilocalorie per mole (kcal/mol). Converting between the two goes through the Avogadro constant (NA = 6.022 * 10^23 mol^-1) – so "1 eV" as a molar quantity is not the same as "1 eV" per individual particle, but corresponds to 1 eV * NA.

Key conversion factors:

  • 1 hartree (Eh) = 2,625.50 kilojoule per mole (kJ/mol) = 627.51 kcal/mol – standard unit in quantum chemistry calculations
  • 1 electronvolt (eV) = 96.485 kilojoule per mole (kJ/mol) – converted to a molar basis via NA
  • 1 rydberg (Ry) = 1,312.75 kilojoule per mole (kJ/mol) – equals ½ hartree
  • 1 wavenumber (cm^-1) = 0.011963 kilojoule per mole (kJ/mol) – common in vibrational spectroscopy (IR, Raman)
  • 1 kilocalorie per mole (kcal/mol) = 4.184 kilojoule per mole (kJ/mol)

Applications:

  • Quantum chemistry: converting calculation results (usually in hartree) into more interpretable kJ/mol or kcal/mol
  • Spectroscopy: converting wavenumbers (cm^-1) from IR or Raman spectra into energy units
  • Thermodynamics: comparing bond, activation, and reaction energies across different units

The molar/atomic energy converter helps interpret quantum chemistry results and spectroscopic data. For energy in the classical, non-molar sense (joule, kilocalories, kWh), use the energy converter; for molar mass, the molar mass converter.

Frequently asked questions about converting molar/atomic energy

1 hartree (Eh), the atomic unit of energy in quantum chemistry, equals 2,625.50 kilojoule per mole (kJ/mol), or 627.51 kilocalorie per mole (kcal/mol). This factor is frequently needed to convert results from quantum chemistry calculations into more interpretable energy units.

1 electronvolt (eV) equals 96.485 kilojoule per mole (kJ/mol). The factor comes from the Avogadro constant (N_A): an eV is the energy of a single particle, and multiplying by N_A gives the corresponding molar quantity.

Electronvolt (eV) and hartree are energy per individual particle (electron, molecule), while kJ/mol and kcal/mol give energy per mole of particles. Converting between the two uses the Avogadro constant – so for molar quantities, it must be clear whether a value is meant per particle or per mole.