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Magazine Chapter 4: Q54E (page 717)
The ammonia moleculehas a dipole moment of. Ammonia molecules in the gas phase are placed in a uniform electric fieldwith magnitude. (a) What is the change in electric potential energy when the dipole moment of a molecule changes its orientation with respect tofrom parallel to perpendicular? (b) At what absolute temperature T is the average translational kinetic energyof a molecule equal to the change in potential energy calculated in part (a)? (Note: Above this temperature, thermal agitation prevents the dipoles from aligning with the electric field.)
Short Answer
a) The change in electric potential is
b) The Absolute Temperature T is 0.39K.
Step by step solution
Potential Energy of a dipole
The initial energy is given by;
Change in electric potential energy
The change in the electric potential between the final and the initial position,
Therefore, the initial energy is;
As the angle between the p and E is 0,
Therefore, potential is 
Now the change in electric potential energy is;
Hence, the change in electric potential is 
Absolute temperature T
As the change is K.E is equivalent to the change in P.E
k is Steven-Boltzmann constant.
On putting the value;
Hence, the Absolute Temperature T is 0.39K.
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