What am I doing wrong here?!!!

[BlondeChick]

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What is the energy (in kilojoules per mole) of photons corresponding to the shortest-wavelength line in the Lyman series for hydrogen?

Okay...... as you geniuses already know, the Lyman series is just a special case of the Balmer-Rydberg equation:

1/lambda = R [(1/m^2) - (1/n^2)] OR v = R times c[(1/m^2) - (1/n^2)]

where lambda is the wavelength, measured in nanometers, R is a constant that equals 1.097 X 10^2 nm^-1, and c is the speed of light, 3.00 X 10^8 m/s, and v is the frequency measured in s^-1, or hertz (same thing).

for the lyman series, m = 1. The shortest-wavelength line in the lyman series will give an n value of infinity ... since i want to find the wavelength, and i'm using the equation E = hv, i'd obviously use this here equation, v = R times c[(1/m^2) - (1/n^2)], to find the frequency associated with the shortest wavelength line in the lyman series. okay, so when i plug everything in, this is what i get for v:

v = (1.097 X 10^-2 nm^-1) (3.00 X 10^8 m/s) = 3.29 X 10^14 s^-1
---------------------
10^-9 m/ nm

okay......... and the last part: E = hv, where h is a constant equal to 6.626 X 10^-34 J/s:

i get a final answer of 1.34 X 10-4 kJ/mol. The right answe is 1310 kJ/mol.

 

[DrChandy]

What is the energy (in kilojoules per mole) of photons corresponding to the shortest-wavelength line in the Lyman series for hydrogen?

Okay...... as you geniuses already know, the Lyman series is just a special case of the Balmer-Rydberg equation:

1/lambda = R [(1/m^2) - (1/n^2)] OR v = R times c[(1/m^2) - (1/n^2)]

where lambda is the wavelength, measured in nanometers, R is a constant that equals 1.097 X 10^2 nm^-1, and c is the speed of light, 3.00 X 10^8 m/s, and v is the frequency measured in s^-1, or hertz (same thing).

for the lyman series, m = 1. The shortest-wavelength line in the lyman series will give an n value of infinity ... since i want to find the wavelength, and i'm using the equation E = hv, i'd obviously use this here equation, v = R times c[(1/m^2) - (1/n^2)], to find the frequency associated with the shortest wavelength line in the lyman series. okay, so when i plug everything in, this is what i get for v:

v = (1.097 X 10^-2 nm^-1) (3.00 X 10^8 m/s) = 3.29 X 10^14 s^-1
---------------------
10^-9 m/ nm

okay......... and the last part: E = hv, where h is a constant equal to 6.626 X 10^-34 J/s:

i get a final answer of 1.34 X 10-4 kJ/mol. The right answe is 1310 kJ/mol.

Use E=(hc)/lambda.

Using this formula, substitute for c (and) lambda, in terms of "R, m, n (and v [in the case of c])". You should get E=hv, which it appears that you did.

Now solve E=hv, using the v value of "v = R times c[(1/m^2) - (1/n^2)]"

That should give you the answer.