General Chemistry Lab

Question

The IR spectrum of ethyl alcohol contains a peak at wavenumber 3362 cm-1 that corresponds to the O-H bond stretch. What is the wavelength in μm for this bond stretch in ethyl alcohol? What is the energy value that corresponds to this bond stretching in one molecule (in Joules)?

Answer 1

To convert 3362 cm^-1 to um we do as follows:

10,000 / 3362 = 2.97 um because wavelength in um = 10,000 / cm^-1

So, the wavelength in um = 2.97 um

E = hc/λ

E = energy = ?

h = Planck's constant = 6.626x10^-34 Jsec

c = speed of light = 3x10⁸ m/sec

λ = wavelength = 2.97 um (but we will convert to meters to be consistent with units of c)

2.97 um x 1 m / 1x10⁶ um = 2.97x10^-6 m

E = (6.626x10^-34 Jsec)(3x10⁸ m/sec) / 2.97x10^-6 m = 6.69x10^-20 J