Electronvolts to Kilocalories per Mole Converter
Common Conversions
| eV/particle | kcal/mol |
|---|---|
| 0.01 | 0.231 |
| 0.025 | 0.577 |
| 0.1 | 2.306 |
| 0.5 | 11.53 |
| 1 | 23.061 |
| 2 | 46.121 |
| 3 | 69.182 |
| 4 | 92.242 |
| 5 | 115.303 |
| 10 | 230.605 |
| 13.6 | 313.623 |
Why this conversion matters in chemistry
Photocatalysis crosses this conversion every time band-gap energetics meet thermal-activation barriers. A 3.2 eV TiO₂ anatase band gap is 73.8 kcal/mol — a meaningful number to compare against a typical 20–40 kcal/mol activation energy for a dark catalytic step. The constant of 23.0605 kcal/mol per eV comes from 1 eV × Avogadro's number = 96.485 kJ/mol, divided by 4.184 J/cal. It comes up when computational-chemistry output (in eV or hartree) needs to be in the kcal/mol form experimental thermodynamic data uses.
Formula
Where the factor comes from
Read the units on the two sides carefully: electronvolts per particle on the left, kilocalories per mole on the right. Avogadro's number is doing work here that no ordinary prefix does, which makes this a change of basis rather than a plain unit conversion. Start from the exact joule value of the electronvolt, 1.602176634 × 10⁻¹⁹ J, multiply by Nₐ = 6.02214076 × 10²³ mol⁻¹ — also exact since 2019 — and the product is 96485.3321233100184 J per mole per volt. Divide by 4.184 J/cal for calories, then by 1000 for the kilo, and 23.0605478… kcal/mol per eV drops out. Every input is defined, so the factor is an exact rational; the calorie step is what stops its decimal from terminating.
Precision and significant figures
Four figures, 23.06, cover essentially everything, because the eV going in is seldom better than three. A DFT reaction energy converges to perhaps 0.01 eV against basis set and grid, which is 0.2 kcal/mol, while the systematic error of a given functional against experiment runs several times that. The 1 kcal/mol accuracy target quoted throughout the computational literature corresponds to 0.043 eV, so the factor's own digits become irrelevant long before they run out. Rounding all the way to 23 costs 0.26 percent — acceptable for a scale check, not for a barrier you intend to tabulate.
Worked Examples
The conversion anchor — useful as a mental factor for any quick scale check.
A moderate activation-energy barrier, the kind a kinetics study reports.
About the C–H bond dissociation energy in methane — useful as a strong-bond reference.
kT at room temperature — the thermal-energy floor below which barriers are easily crossed.
Common mistakes
Avogadro is already inside the 23.06
The factor carries a per-particle energy to a per-mole one in a single step. Apply it to something already per mole — a kJ/mol barrier divided into eV, then converted back — and Nₐ enters twice. The units are the guard here: eV on the input side has to mean eV per atom, molecule or photon, and never eV per mole.
0 K electronic energies against 298 K enthalpies
A converted calculation is usually a bare electronic energy difference at 0 K, with no zero-point vibrational contribution and no thermal correction applied. Tabulated kcal/mol values are typically enthalpies at 298 K. The two can differ by several kcal/mol on the same reaction, and no care taken over the unit conversion closes that gap; the corrections have to be computed and added before any comparison means something.
Reading kcal/mol back onto one molecule
A 78 kcal/mol bond dissociation energy describes a mole of bonds. Photochemistry asks whether one photon can break one bond, which is a per-particle question, and answering it means going back to eV by dividing by 23.06. Sliding between the two framings is how a photon of ample energy gets declared insufficient, or an inadequate one gets waved through.