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Topic: Help with CHEM 115 Problem  (Read 255 times)

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Offline JesseTCarter

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Help with CHEM 115 Problem
« on: September 07, 2019, 06:47:09 PM »
I have two problems that I’ve been struggling with and I was wondering if I could get some guidance with them. Thank you!


You have a 5.58 g sample of phosphorus. If each atom in this sample is excited through heating and then emits a 383 nm photon:

What is the energy of each photon?
How many photons are emitted in total?
What is the total energy of light emitted?

I have the energy of each photon as 5.19e-19J

I can’t figure out the other two, or how to go about answering them.

Offline Borek

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Re: Help with CHEM 115 Problem
« Reply #1 on: September 07, 2019, 07:06:48 PM »
Hint: moles to atoms.
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Offline JesseTCarter

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Re: Help with CHEM 115 Problem
« Reply #2 on: September 07, 2019, 08:01:01 PM »
I did that, but I'm not sure how to use it to get the other two answers. Molar mass of Phosphorus is 30.974amu. You take the grams and times it by Avogadro's number and divide that by the amu to get atoms which = 1.084869891e23

I'm just not sure how to use this number from here. It's probably super simple and I'm over complicating it lol.

Offline JesseTCarter

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Re: Help with CHEM 115 Problem
« Reply #3 on: September 07, 2019, 08:08:11 PM »
1.08e23 is the second answer, alright. That's good to know. Now total energy...

Offline JesseTCarter

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Re: Help with CHEM 115 Problem
« Reply #4 on: September 07, 2019, 08:18:09 PM »
I have the total energy as 56052J but the website is not taking my answer and it's starting to frustrate me lmao.

Offline Vidya

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Re: Help with CHEM 115 Problem
« Reply #5 on: September 08, 2019, 02:31:52 AM »
Convert grams of phosphorus into moles of phosphorus. As each photon is needed to excite every atom so get the number of phosphorus atoms and that will be the total number of photons needed.
now energy of each photon is given multiply this energy with total number of photos to get the total amount of energy required to excite phosphorus atoms of the given amount


Offline Borek

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Re: Help with CHEM 115 Problem
« Reply #6 on: September 08, 2019, 03:35:03 AM »
I have the total energy as 56052J but the website is not taking my answer and it's starting to frustrate me lmao.

That's close to the correct answer, most likely the site expects you to use correct number of significant figures or to enter the answer in a scientific format.
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