Absolute temperature for average translational kinetic energ

[rsatchel]

Homework Statement

The ammonia molecule (NH3) has a dipole moment of 5.0×10−30C⋅m. Ammonia molecules in the gas phase are placed in a uniform electric field E⃗ with magnitude 1.3×106 N/C .

Part A:
What is the change in electric potential energy when the dipole moment of a molecule changes its orientation with respect to E⃗ from parallel to perpendicular?

Part B:
At what absolute temperature T is the average translational kinetic energy 3/2 kT of 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.)

Homework Equations

U = -p . E
T = p X E

The Attempt at a Solution

[/B]
I got Part A:
delta U = p. E = p E cos theta = (5.0E-30)(1.3E6) = -6.5E-24 J,

so delta U = 6.5E-24J

Part B:

My reasoning is as follows:
KE + PE = 0
3/2 kT + U = 0
U = -3/2 kT
(-2/3 U) / k = T
T = (-2/3)(6.5E-24) / (8.99E9) = 482E-36 degrees K

which is wrong.
I don't know what I'm doing wrong :/

 

[DrClaude]

What is k and what is its value?

 

[rsatchel]

What is k and what is its value?

I thought it was maybe: k = 8.99E9 Nm^2/C^2

 

[BrazenArm]

Use Boltzmann constant for k, it is approximately 1.38*10^-23 J/K