Question

The human eye contains a molecule called 11-cis-retinal that changes shape when struck with light of sufficient energy. the change in shape triggers a series of events that results in an electrical signal being sent to the brain. the minimum energy required to change the conformation of 11-cis-retinal within the eye is about 165 kj/mol. calculate the longest wavelength of light visible to the human eye. (avogadro's number is 6.022 x 1023 units/mole)

Answer 1

725 nm The energy needed for a single molecule to change will be the energy for a mole to change divided by avogadro's number, so 165000 / 6.022 x 10^23 = 2.74x10^-19 J The energy of a photon is expressed as E = hc/l where E = energy h = Planck constant (6.626070040Ă—10^â’34 Js) c = speed of light (299792458 m/s) l = wavelength Now solve for l E = hc/l El = hc l = hc/E Now substitute known values. l = hc/E l = 6.626070040Ă—10^â’34 Js * 299792458 m/s / 2.74x10^-19 J I = 7.25x10^-07 m l = 725 nm