# Photon Energy Calculator

Calculate photon energy from wavelength or frequency using E = hc/λ. Get results in joules, electron volts, and kJ/mol with spectral region.

## What this calculates

Calculate the energy of a photon from its wavelength or frequency using the Planck-Einstein relation E = hf = hc/λ. Results are given in joules, electron volts (eV), and kilojoules per mole, with automatic identification of the electromagnetic spectral region.

## Inputs

- **Calculate From** — options: Wavelength, Frequency — Choose whether to input wavelength or frequency.
- **Wavelength** (nm) — min 0 — Wavelength of the photon in nanometers (visible light: 380-750 nm).
- **Frequency** (Hz) — min 0 — Frequency of the photon in hertz.

## Outputs

- **Energy** (J) — Energy of a single photon in joules.
- **Energy** (eV) — Energy of a single photon in electron volts.
- **Energy per Mole** (kJ/mol) — Energy per mole of photons (Avogadro's number of photons).
- **Frequency** (Hz) — Frequency of the photon.
- **Wavelength** (nm) — Wavelength of the photon.
- **Spectral Region** — formatted as text — Region of the electromagnetic spectrum.

## Details

The energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength, as described by the Planck-Einstein relation: E = hf = hc/λ, where h is Planck's constant (6.626 × 10⁻³⁴ J·s), f is frequency, c is the speed of light (2.998 × 10⁸ m/s), and λ is wavelength.

This relationship is fundamental to quantum mechanics and explains many phenomena including the photoelectric effect, atomic emission spectra, and spectroscopy. Higher-frequency (shorter-wavelength) photons carry more energy — ultraviolet photons are energetic enough to break chemical bonds, while infrared photons cause molecular vibrations that we feel as heat.

In chemistry, photon energy calculations are essential for spectroscopy (UV-Vis, IR, NMR), photochemistry, and understanding electronic transitions in atoms and molecules. The energy per mole of photons tells chemists whether light of a given wavelength has sufficient energy to drive a photochemical reaction, break a specific bond, or excite an electron to a higher orbital.

## Frequently Asked Questions

**Q: What is Planck's constant?**

A: Planck's constant (h) is a fundamental constant of quantum mechanics with a value of 6.626 × 10⁻³⁴ J·s. It relates the energy of a photon to its frequency through E = hf. Its reduced form, ħ = h/(2π), appears in many quantum mechanical equations. Planck's constant sets the scale at which quantum effects become important.

**Q: What is an electron volt (eV)?**

A: An electron volt is the amount of kinetic energy gained by a single electron when accelerated through an electric potential difference of one volt. It equals 1.602 × 10⁻¹⁹ joules. The eV is a convenient unit for atomic and molecular energies because the joule is impractically large at the quantum scale. Visible light photons have energies of about 1.6 to 3.3 eV.

**Q: Why is energy given per mole of photons?**

A: A single photon has an extremely small energy (on the order of 10⁻¹⁹ J), which is difficult to relate to macroscopic chemistry. Multiplying by Avogadro's number (6.022 × 10²³) gives the energy per mole of photons in kJ/mol, which can be directly compared to bond dissociation energies and reaction enthalpies.

**Q: What wavelength range is visible light?**

A: Visible light spans wavelengths from about 380 nm (violet) to 750 nm (red). This corresponds to frequencies of roughly 4.0 × 10¹⁴ Hz to 7.9 × 10¹⁴ Hz and photon energies of about 1.65 to 3.26 eV. The human eye is most sensitive to green-yellow light at around 555 nm.

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Source: https://vastcalc.com/calculators/chemistry/photon-energy
Category: Chemistry
Last updated: 2026-04-21