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Joules to Electronvolts Converter
↔ Convert eV to J instead

Common Conversions

J eV
1.602e-19 1
3.204e-19 2
4.806e-19 3
8.01e-19 5
1.602e-18 10
2.18e-18 13.6
1.602e-17 100
1.602e-16 1000

Why this conversion matters in chemistry

Photochemistry reports pulse energies in joules — a typical 248 nm excimer laser pulse might deliver 500 mJ — but what matters for molecules is the energy per photon, which lives at the eV scale. 500 mJ of 248 nm light contains about 6.24 × 10¹⁷ photons at 5.00 eV each, calculated from hc/λ. Dividing the total pulse energy by the per-photon energy (in joules, via 1 eV = 1.602 × 10⁻¹⁹ J) gives you the photon count — the input for any quantum-yield calculation in a photochemistry experiment. The conversion bridges two natural scales: joules for bulk energy delivered, eV for what individual molecules absorb.

Formula

eV = J ÷ 1.602176634 × 10⁻¹⁹

Worked Examples

1.602 × 10⁻¹⁹ J = 1 eV

The defining equivalence — the energy one electron gains falling through a 1 V potential, expressed in SI.

2.18 × 10⁻¹⁸ J = 13.6 eV

Hydrogen's ionization energy. The Rydberg — arguably the most memorable per-particle energy in atomic chemistry.

3.0 × 10⁻¹⁹ J = 1.87 eV

A red photon near 660 nm. In the visible range, this is the low-energy end.

5.0 × 10⁻¹⁹ J = 3.12 eV

A violet photon near 400 nm — right at the visible/UV boundary. Enough energy to break some weak bonds.

Frequently Asked Questions

How do I convert joules to electronvolts?
Divide by 1.602176634 × 10⁻¹⁹. So 2.18 × 10⁻¹⁸ J becomes 13.6 eV, which is hydrogen's ionization energy. The factor is the elementary charge in coulombs — not a coincidence, but the definition of the electronvolt.
Why do electronvolts show up in chemistry?
Because atomic and molecular energies land naturally in the 1–25 eV range. Ionization energies, electron affinities, per-bond dissociation energies, photon energies across the visible and UV — all fit into single or low double digits in eV. The same values in joules come out as unwieldy 10⁻¹⁹ numbers that are much harder to compare at a glance.
How do eV relate to kJ/mol?
Multiply eV by 96.485 to get kJ/mol. The factor is Faraday's constant divided by 1000 — essentially Avogadro's number times the elementary charge. A 5 eV bond energy works out to 482 kJ/mol, which lands it in the typical range for single covalent bonds.
What's the energy range of visible light in eV?
About 1.77 eV at the red end (700 nm) to 3.1 eV at the violet end (400 nm). UV photons are above 3.1 eV, which is why UV light can break some weaker chemical bonds that visible light can't touch.