## jennilalala 2 years ago Calculate the energy in J of 0.32 moles of photons whose frequency is 2.6 x 10^15 ?

1. SheldonEinstein

You must know the formula for calculating the energy... in this situation. Do you know the formula?

2. aaronq

E=hv h is planks constant v= frequency this gives you the energy of 1 photon so multiply this by the amount of photons you have: amount of photons = avogadros constant x number of moles

3. SheldonEinstein

that v is actually "new (pronounced as new)"

4. SheldonEinstein

So @jennilalala with the help of : E = hv formula, can you find the energy by putting the values given ?

5. SheldonEinstein

"v" --> $$\large{\color{blue}{\nu}}$$ .... right @aaronq ?

6. jennilalala

I am back sorry ahaah. yes i know the formulas. i just dont know what to do if it says ".32 moles of photon.."

7. SheldonEinstein

Do you the planck's constant ?

8. jennilalala

6.626x10^23 ?? not by heart...yet...

9. aaronq

haha yep, v= "new"

10. jennilalala

10^-34

11. SheldonEinstein

OK so it is $\large { h = 6.626 \times 10^{-34} m^{-1}}$

12. SheldonEinstein

oh wait it is m^2 kg/s

13. SheldonEinstein

So right, now solve this : $\large{E = 6.626 \times 10^{-34} \times 2.6 \times 10^{15}}$ What do you get?

14. jennilalala

1.73x10^-18

15. SheldonEinstein

My calculator says it as : $$\large{\color{blue}{ 17.2276 * 10^{-19}}}$$ that is 1.72276 * 10^{-18}

16. SheldonEinstein

OK so now .. this is the energy for $$1$$ photon ... now we to calculate for 0.32 moles of photons.

17. SheldonEinstein

See ... no. of photons = Avogadros's constant * no. of moles of photons...

18. SheldonEinstein

19. jennilalala

6.022x10^23

20. SheldonEinstein

Good! So now, solve this one : $\large{\color{red}{\mathbb{No. of Photons}} = \color{blue}{6.022 * {10}^{23}} \times \color{green}{0.32}}$

21. jennilalala

1.93x10^23

22. jennilalala

then i multiply the two calculations?

23. SheldonEinstein

Correct! So this is your No. of photons. Now multiply this result with "1.73 * 10^{-18} "

24. jennilalala

3.3x10^-5

25. SheldonEinstein

Right!

26. jennilalala

not negative typo lol

27. SheldonEinstein

No problem.

28. SheldonEinstein

So finally you have your correct way, I hope you got it ?

29. jennilalala

Yes thank you so much!

30. SheldonEinstein

You're welcome @jennilalala . keep up the good work.