HW 2 ch1 1.51

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Jeremiah Hutauruk
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HW 2 ch1 1.51

Postby Jeremiah Hutauruk » Sun Oct 14, 2018 5:08 pm

It says " Infrared spectroscopy is an important tool for studying vibrations of molecules. Just as an atom can absorb a photon of suitable energy to move an electron from one electronic state to another, a molecule can absorb a photon of electromagnetic radiation in the infrared region to move from one vibrational energy level to another. In infrared spectroscopy, it is common to express energy in terms of /c, with the units cm 1 (read
as reciprocal centimeters). (a) If an absorption occurs in the infrared spectrum at 3600 cm 1, what is the frequency of radiation that corresponds to that absorption? (b) What is the energy, in joules (J), of that absorption? (c) How much energy would be absorbed by 1.00 mol of molecules absorbing at 3600 cm 1?"

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Re: HW 2 ch1 1.51

Postby Chem_Mod » Sun Oct 14, 2018 6:38 pm

Start by converting inverse cm to cm, then to meters to get wavelength.

Claudia Luong 4K
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Re: HW 2 ch1 1.51

Postby Claudia Luong 4K » Sun Oct 14, 2018 8:56 pm

The problem states that in infrared spectroscopy, we express energy in terms of v /c.
Therefore, for part (a), v/c = 3600 cm^-1
v = (c)(3600cm^-1) = (2.997 x 10^8 m/s)(3600cm^-1)
After this, convert the value for c into terms of cm/s in order to cancel out the units, and you should be left with a value of Hz for the frequency.

b) Plug in the value for frequency that you just found from part a) and Planck's constant, 6.626 x 10^-34 Js, into the formula E=hv to find the energy of that absorption.

c) Convert 1.00 mol to molecules by using Avogadro's number. In part (b), we found the energy absorbed per molecule, so we can multiply this value by the number of molecules to get the final answer.

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