Problem B9

[Jasmin Argueta 1K]

For problem B9 part B I don't understand the thought process behind multiplying 1.41x10^20(amount of moles per two seconds) by 1 mole then dividing by 6.022x10^23. I would have thought to use the amount of photons per ONE second not two seconds then multiply by 1 mole and divide by 6.022x10^23. Can someone please explain their though process for knowing how to do this. Thank you!

[Chem_Mod]

The question is asking how many moles of photons are emitted during the 2 second interval. To do that, you must first find the # of photons emitted in the 2 second interval, and then using Avogadro's number, you can convert that to moles.

[Courtney Quan 1C]

Hi! 1.41x10^20 actually refers to the number of photons (emitted by the light in 2 seconds) instead of the amount of moles per 2 seconds. Because you already have the number of photons, you just need to convert it to moles- you already calculated the number of photons emitted in 2 seconds so you don't have to worry about the 2 seconds anymore. So we multiply 1.41x10^20 photons by 1 mole/6.02x10^23 photons to convert it to moles, which should give you 2.3x10^-4 mol photons.

The reason why we don't use the amount of photons per ONE second is because the question is still asking about the number of moles emitted during that time interval, which is 2 seconds. Having found the number of photons emitted in 2 seconds (1.41x10^20), all you have to do is convert that number to moles by multiplying it by 1 mol/6.02x10^23 photons to get the right answer.

Hope this helps!

[Daniel Chang 3I]

the 1.41x10^20 refers to the number of photons and you would then multiply that number with Avogadro's number

[Jasmin Argueta 1K]

Why aren't the 2 seconds taken into consideration in part A?