In a crude model of a rotating diatomic molecule of chlorine, the two chlorine atoms are apart and rotate about their
center of mass with angular speed . What is the rotational kinetic energy of one molecule of Cl2 which has a molar mass of 70g/mol?
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<p>moment of inertia , I = 2(mr<sup>2</sup>) = 2mr<sup>2</sup></p>
<p>Here , <img alt="m=\frac{70\times10^{-3}}{2\times6.02\times10^{23}}=5.81\times10^{-26}kg" src="https://latex.codecogs.com/gif.latex?m%3D%5Cfrac%7B70%5Ctimes10%5E%7B-3%7D%7D%7B2%5Ctimes6.02%5Ctimes10%5E%7B23%7D%7D%3D5.81%5Ctimes10%5E%7B-26%7Dkg" /></p>
<p>and <img alt="r=\frac{2.0\times10^{-10}}{2}=1\times10^{-10}m\\ \therefore l=2(5.81\times10^{-26})(1\times10^{-10})^{2}=1.16\times10^{-45}kgm^{2}" src="https://latex.codecogs.com/gif.latex?r%3D%5Cfrac%7B2.0%5Ctimes10%5E%7B-10%7D%7D%7B2%7D%3D1%5Ctimes10%5E%7B-10%7Dm%5C%5C%20%5Ctherefore%20l%3D2%285.81%5Ctimes10%5E%7B-26%7D%29%281%5Ctimes10%5E%7B-10%7D%29%5E%7B2%7D%3D1.16%5Ctimes10%5E%7B-45%7Dkgm%5E%7B2%7D" /></p>
<p><img alt="K_{R}=\frac{1}{2}lw^{2}=\frac{1}{2}\times(1.16\times10^{-45})\times(2\times10^{12})^{2}=2.32\times10^{-21}g" src="https://latex.codecogs.com/gif.latex?K_%7BR%7D%3D%5Cfrac%7B1%7D%7B2%7Dlw%5E%7B2%7D%3D%5Cfrac%7B1%7D%7B2%7D%5Ctimes%281.16%5Ctimes10%5E%7B-45%7D%29%5Ctimes%282%5Ctimes10%5E%7B12%7D%29%5E%7B2%7D%3D2.32%5Ctimes10%5E%7B-21%7Dg" /></p>
<p>At T= 300K,rotational K.E. should be equal to <img alt="\frac{1}{2}kT" src="https://latex.codecogs.com/gif.latex?%5Cfrac%7B1%7D%7B2%7DkT" /></p>
<p><img alt="=\frac{1}{2}\times(1.38\times10^{-23})\times300=2.07\times10^{-21}g" src="https://latex.codecogs.com/gif.latex?%3D%5Cfrac%7B1%7D%7B2%7D%5Ctimes%281.38%5Ctimes10%5E%7B-23%7D%29%5Ctimes300%3D2.07%5Ctimes10%5E%7B-21%7Dg" /></p>
<p> </p>