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Finding the Spring Constant - Help! Algebra Issues!

  1. Dec 4, 2006 #1
    Finding the Spring Constant -- Help! Algebra Issues!

    Molecular bonds can be treated like springs. From the vibrational frequencies of the bonds, one can determine the appropriate spring constants. Hydrogen, H2, has a vibrational frequency of 1.3192 X 1014Hz. Deuterium, D2, is an isotope of hydrogen and is twice as massive as hydrogen. It has a vibrational frequency of 0.9345 X 1014Hz. Do these molecules have the same spring constant? Explain.

    I used the equations

    T=2pi * square root m/k
    F = 1/T

    From the second equation, I got T=1/F. Since I know F of both bonds, I can find T.

    For H2, T = 7.58X10^-15 and for D2 T= 1.07X10^-14.

    mass for H2 is just m and mass for D2 is 2m

    I plugged all these expressions into T=2pi*square root m/k, and isolated k, and got H2 to equal 6.87X10^29 and D2 to be 6.896X10^29. So they are only about .03 off which I think is pretty close to having pretty much the same spring constant. What I had problems with, was I am not sure whether I did the correct algebra for isolating k. Also, does it seem like I am approaching this problem correctly? Thanks!
  2. jcsd
  3. Dec 4, 2006 #2


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    Homework Helper

    Your approach looks okay, and the solution should be too, under the assumption you did the algebra correctly and plugged in the appropriate masses of the isotopes.
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