- #1

rsatchel

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## 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 :/