Question

A laser is emitting photons with a wavelength of 639.8 nm. What is the energy for 1 mole of these photons? For Planck's constant, use a value of 6.626x10-34 J s. Use units of kJ/mol. Report just the number, not the units.

Answer 1

Answer:

The energy for 1 mole of these photons is E = 31 × $10^{-23}$ $\frac{KJ}{mol}$  

Explanation:

Given data

Wavelength $\lambda =$ 639.8 × $10^{-9}$ m

Plank constant h = 6.626 × $10^{-34}$ J sec

Speed of light c = 3 × $10^{8}$ meter per second

We know that Energy  of a photon is given by

$E = \frac{h c}{\lambda}$

Value of ( h c ) = 6.626 × $10^{-34}$  × 3 × $10^{8}$ = 19.878 × $10^{-26}$

$\lambda =$ 639.8 × $10^{-9}$ m

Now Energy  of a photon

$E =( \frac{19.878}{639.8}) 10^{-17}$

E = 0.031 × $10^{-17}$ Joule per mole

E = 31 × $10^{-23}$ $\frac{KJ}{mol}$  

Therefore the energy for 1 mole of these photons is E = 31 × $10^{-23}$ $\frac{KJ}{mol}$