The following question was asked by me:The dissociation energy of H2 is 430.53 KJ/mol. If H2 is exposed to radiant energy of wavelength 253.7 nm, what % of radiant energy will be converted into KE?ask iitian expert ramesh.iitkgpreplied as:The bond dissociation energy for the H-H bond is the energy required to break the H2 molecule (in its most stable geometry) into separate hydrogen atoms.Radiant energy = 1242 eV-nm / 253.7 nm = 4.895 eV = 7.843x10-19 J. How this Radiant Energy = 1242 eV-nm/253.7 nm came? Explain in detail...

I assumed you (a JEE prep. student), might be knowing that the product of Plank's constant and velocity of light can be expressed as :                    hc = 1242 eV-nm  and    1 eV = 1.602x10^-19 J

and   E = h.c / wavelength

Please check the units..

I hope this makes you clear...

Radiant energy = 1242 eV-nm / 253.7 nm = 4.895 eV = 7.843x10^-19 J. How this Radiant Energy = 1242 eV-nm/253.7 nm

While solving numbers of problems, it didn't click in my mind. We were not told about it in coaching class nor I saw in book. Thanks..this formula is of great use!