Kilocalories per Mole to Electronvolts Converter
Common Conversions
| kcal/mol | eV/particle |
|---|---|
| 0.1 | 0.00434 |
| 0.6 | 0.026 |
| 1 | 0.04336 |
| 5 | 0.2168 |
| 10 | 0.4336 |
| 23.06 | 1 |
| 50 | 2.168 |
| 100 | 4.336 |
| 150 | 6.505 |
| 200 | 8.673 |
| 313.6 | 13.6 |
Why this conversion matters in chemistry
Take dFT versus experiment benchmarking. A 104 kcal/mol C–H bond dissociation energy in methane is 4.51 eV per bond — the form a Pt(111) surface-scattering study reports its dissociation barrier in. The conversion is the routine bridge between NIST thermochemistry tables and surface-science experimental data. A factor of 0.043364 eV per kcal/mol is the inverse of 23.0605, which itself is Avogadro's number divided by the J/eV definition. In practice you reach for it when per-mole thermodynamic data has to be expressed in per-particle electron-energy units.
Formula
Where the factor comes from
Two of the three inputs to this factor became exact only in 2019. Before the SI redefinition it inherited the experimental uncertainty of the Avogadro constant and the elementary charge; both are now fixed numbers, Nₐ = 6.02214076 × 10²³ mol⁻¹ and e = 1.602176634 × 10⁻¹⁹ C, so nothing measured survives anywhere in the chain. The third input, 4184 J per thermochemical kilocalorie, was stipulated decades earlier. Running it through: 4184 J/mol ÷ Nₐ gives 6.9477 × 10⁻²¹ J for one particle, and dividing that by the joule value of the electronvolt gives 0.0433641 eV. The reciprocal, 23.0605 kcal/mol per eV, is the form most people keep in their heads. Fixing the constants shifted the number by less than its own former uncertainty, so no published value needed restating.
Precision and significant figures
Four figures, 0.04336, is more than either side of this conversion usually repays. Thermochemical tables give bond and formation energies to a few tenths of a kilocalorie per mole at best; 0.3 kcal/mol is 0.013 eV, so the tabulated uncertainty arrives orders of magnitude coarser than anything the fourth digit of the factor decides. On the eV side, photoelectron and electron-energy-loss measurements resolve to tens of millielectronvolts, and a tenth of an eV is already 2.31 kcal/mol, larger than most of the thermochemical disagreements anyone would be trying to settle. Rounding the factor to 0.0434 costs 0.08 percent and 0.043 costs 0.84 percent. Neither buys anything, and the second is big enough to surface in a barrier comparison.
Worked Examples
The reverse anchor — about how many kcal/mol make an eV per particle.
The conversion anchor — useful for any per-mole to per-particle conversion.
About a typical strong-bond dissociation energy expressed per particle.
About kT at room temperature — the per-particle thermal-energy floor.
Common mistakes
The reciprocal used as a multiplier
Both 0.043364 and 23.0605 belong to this pair, and putting the second where the first goes overshoots by a factor of 532. A 100 kcal/mol bond energy then arrives as 2306 eV instead of 4.34 eV — implausible enough to catch, provided someone looks. Keep a scale anchor handy: chemical bonds live between roughly 1 and 10 eV per particle.
Volts and electronvolts read off each other
A cell potential in volts is numerically the energy per electron in electronvolts, which tempts people to treat the two as one quantity. Energy per formula unit is n times the potential. A two-electron process at 1.23 V carries 2.46 eV, which is 56.7 kcal/mol, not 28.4. The electron count has to be settled before this factor touches anything.
Hartrees fed in as kcal/mol
Electronic-structure output frequently arrives in hartrees or rydbergs rather than electronvolts, and one hartree is about 27.2114 eV. That relation rests on the Rydberg constant and is measured, unlike everything else on this page. Dropping a hartree total into a kcal/mol field and multiplying by 0.043364 produces a number with no interpretation at all.