Calculte the Energy of 1 mole of photons - Help

[lucky_star]

Calculte the Energy of 1 mole of photons - Help!

Homework Statement

Calculate the energy, in kilojoules, of one mole of photons of yellow laser light of wavelength 570 nm.

The correct answer is: 2.10x10²

Homework Equations

Ephoton= hc/wavelength

The Attempt at a Solution

Step by step:
1. Convert the wavelength of 570nm to m:

10-9m= 1 nm, so:

570nm * (10-9m) = 5.7E-7 m

2. Ephoton= hc/wavelength

Ephoton= (6.63E-34 * 3.E8)/5.7E-7 m

Ephoton= 3.49E-19 J

3. Finally, I convert to kJ:

Ephoton= 3.49E-19J/1000J = 3.49E-22 kJ

Can someone help me with this problem, I tried many times but I still get the same result.

 

[rock.freak667]

Think of Avogadro's number/constant.

 

[lucky_star]

So, I would have:
3.49E-22 kJ * the Avogadro's constant, which is 6.022 × 10E23 mol^-1
And I got the answer. yoohoo! Thank you so much. Please explain to me why I have to multiply my answer with the Avogadro's constant to get the final answer. I appreciate your help!

 

[rock.freak667]

One mole should contain 6.02E23 elementary units. You found the energy of 1 elementary unit.

 

[lucky_star]

Oh, I forgot that concept. Thanks for reminding me. One mole of any substance contains this many [6.022 × 10E23] units. :D Cheers!