## Fall 2014 Quiz Prep

H-Atom ($E_{n}=-\frac{hR}{n^{2}}$)

Michael Lonsway 3O
Posts: 43
Joined: Wed Sep 21, 2016 2:57 pm

### Fall 2014 Quiz Prep

An excited hydrogen atom emits light with a frequency of 1.14x10^14 Hz to reach energy level for which n=4. In what principle quantum level did the electron begin?

I got n=3 but the answer is n=6. I used the different variations of the Rydberg equation and haven't been able get the right answer.

Chem_Mod
Posts: 17949
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 406 times

### Re: Fall 2014 Quiz Prep

If you read the question carefully, you'll notice that it says the atom emits light; thus, the change in energy between the 2 principal quantum levels must be negative. Try solving the problem with this piece of information, and you'll get n=6 as your answer.

Michael Lonsway 3O
Posts: 43
Joined: Wed Sep 21, 2016 2:57 pm

### Re: Fall 2014 Quiz Prep

I put n=4 into n-initial and solved for n-final which allowed me to get n=6. I'm wondering why this worked because the problem asked for the quantum level where the electron began.

Amy_Shao_2D
Posts: 22
Joined: Fri Jul 15, 2016 3:00 am

### Re: Fall 2014 Quiz Prep

Michael Lonsway 4E wrote:I put n=4 into n-initial and solved for n-final which allowed me to get n=6. I'm wondering why this worked because the problem asked for the quantum level where the electron began.

You got the same answer cause you did +deltaE=initial-final, and the actual way is -deltaE=final-initial. Delta E is negative since the problem says the hydrogen atoms emit light, so they're losing energy. Hope that helps!

Diwana Lucero 3K
Posts: 26
Joined: Fri Jul 15, 2016 3:00 am

### Re: Fall 2014 Quiz Prep

I'm also having trouble with this problem and I checked the answer for this, but I don't understand where the En= -2.178 x 10^-18 J came from in the explanation?

Michael Lonsway 3O
Posts: 43
Joined: Wed Sep 21, 2016 2:57 pm

### Re: Fall 2014 Quiz Prep

Thanks for the help! I made Delta E negative since the problem states that energy is emitted and was able to get the right answer.

Rosalva_Mejia_41
Posts: 19
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Fall 2014 Quiz Prep

A problem asks for the energy of a photon emitted with a wavelength of 5.50x10^2. I multiplied it by plank's constant and got the answer. However, I don't understand why that is if the original equations is E= h x frequency, not wavelength.

Wang_Pong_Chan_1L
Posts: 10
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Fall 2014 Quiz Prep

In the Rydberg Equation, does n1 refer to the higher energy level or the lower energy level?

904605949
Posts: 20
Joined: Wed Sep 21, 2016 2:58 pm

### Re: Fall 2014 Quiz Prep

Is number 5 on Quiz 2014 a limiting reactant problem? And also do we have to do/turn in all three of the self-quizes or do we just turn in one? Please help

Pauline Tze 3B
Posts: 57
Joined: Sat Jul 09, 2016 3:00 am
Been upvoted: 1 time

### Re: Fall 2014 Quiz Prep

Wang_Pong_Chan_1L wrote:In the Rydberg Equation, does n1 refer to the higher energy level or the lower energy level?

n1 refers to the initial energy level. Whether it is the higher or lower one depends on the problem.

Pauline Tze 3B
Posts: 57
Joined: Sat Jul 09, 2016 3:00 am
Been upvoted: 1 time

### Re: Fall 2014 Quiz Prep

Rosalva_Mejia_41 wrote:A problem asks for the energy of a photon emitted with a wavelength of 5.50x10^2. I multiplied it by plank's constant and got the answer. However, I don't understand why that is if the original equations is E= h x frequency, not wavelength.

Hi! I'm not understand how you got the answer just by multiplying it by planck's constant because doing that produced 3.64 x 10^-31 which is incorrect.

For this problem you need both E=h x frequency and c= lambda x frequency. Since you're given wavelength, you need to manipulate c= lambda x frequency and plug it into E=h x frequency.
Hope that helps!!

Rosalva_Mejia_41
Posts: 19
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Fall 2014 Quiz Prep

Yea that's what originally did but the workbook had a different answer. Probably a mistake. Thank you.