Einstein
Definition and meaning of Einstein in chemistry.
Einstein is a unit of energy used in photochemistry equal to the energy carried by one mole (6.022 × 10²³) of photons of a given wavelength.
In more detail
Because photon energy depends on wavelength (E = hc/λ), one einstein does not correspond to a fixed number of joules; it must be calculated for the specific light used in a reaction. Chemists use the unit to relate the amount of light absorbed by a photochemical system to the number of moles of product formed, which defines the quantum yield (moles of product per einstein absorbed). The term honors Albert Einstein's 1905 explanation of the photoelectric effect, which established that light energy is quantized into photons.
Key facts
| Field | Physical Chemistry |
|---|---|
| Defines | 1 einstein = 1 mole of photons (6.022 × 10²³ photons) |
| Depends on | Wavelength/frequency of the light (energy is not fixed) |
| Named after | Albert Einstein |
Light at 450 nm has a photon energy of hc/λ ≈ 4.42 × 10⁻¹⁹ J, so one einstein of 450 nm light carries N_A × 4.42 × 10⁻¹⁹ J ≈ 2.66 × 10⁵ J, or about 266 kJ per einstein.
Frequently asked questions
Is the einstein an SI unit?
No. It is a traditional, non-SI unit used mainly in photochemistry literature; energies are more rigorously expressed directly in joules per mole of photons.
How is the einstein used in practice?
It lets chemists express quantum yield as moles of product formed (or reactant consumed) per einstein of light absorbed, allowing comparison of photochemical efficiency across experiments.