Rotational KE Problem

1. Jan 14, 2006

cmilho10

In a crude model of a rotating diatomic molecule of chlorine (Cl2), the two Cl atoms are 2.00x10^-10 m apart and rotate about their center of mass with angular speed = 1.40x10^12 rad/s. What is the rotational kinetic energy of one molecule of Cl2, which has a molar mass of 70.0 g/mol?

I have tried this problem but I really don't even know where to start..

2. Jan 14, 2006

siddharth

What is the forumla for Rotational Kinetic energy of a an object?

3. Jan 14, 2006

cmilho10

KE=1/2* I* (angular speed)^2

I=1/12*m*L^2

would mass=140 g?

4. Jan 14, 2006

siddharth

Why have you chosen I = 1/12* m*l^2? Are you approximating this as a rod of length L? I don't think that's a good idea becuase most of the mass is concentrated in the atom, not the bond. So I think taking this as two sepearate Cl atoms rotating about the COM is a better idea

Also, the mass will not be 140g. The mass of 1 mol of Cl2 is 70 grams. And you know 1 mol of Cl2 contains around 6.023*10^23 molecules. So what is the mass of 1 molecule?

5. Jan 14, 2006

cmilho10

ok i got the mass of one to be 1.16E-22

But then what equation for moment of inertia would I use?