Question

The bright-red color of highway safety flares comes from strontium ions in salts such as Sr(NO3)2 and SrCO3. Burning a flare produces strontium ions in excited states, which then emit red photons at 606 nm and several wavelengths between 636 and 688 nm. Calculate the energy (in Joules per mole) of the 643 nm emission.

Answer 1

We know the formula of Energy

E = h v

= h c /

where v = frequency 1/s

h= planks constant = 6.626 10^-34 J.s

c = speed of light = 3 10⁸ m/s

   = wavelength in m

so formula becomes

E =  6.626 10^-34 J.s 3 10⁸ m/s / (643 10-⁹ m)

= 0.0309 10^-17

= 3.09 10^-19 J

for one mole of photon

E = 6.022 10²³ 3.09 10^-19 J

= 18.6166 10⁴

= 186.166 KJ