# Absolute temperature for average translational kinetic energ

• rsatchel
In summary, the ammonia molecule (NH3) has a dipole moment of 5.0×10−30C⋅m and is placed in a uniform electric field with magnitude 1.3×106 N/C. In Part A, the change in electric potential energy is -6.5E-24 J when the dipole moment changes orientation from parallel to perpendicular. In Part B, the temperature at which the average translational kinetic energy is equal to the change in potential energy is approximately 482E-36 degrees K. The Boltzmann constant (k) is used in the calculation, with a value of approximately 1.38*10^-23 J/K.
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.)

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 :/

What is k and what is its value?

DrClaude said:
What is k and what is its value?

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

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

## What is absolute temperature?

Absolute temperature is a measure of the average kinetic energy of particles in a substance. It is a temperature scale that starts at absolute zero, which is the theoretical lowest possible temperature at which all molecular motion stops.

## How is absolute temperature different from other temperature scales?

Absolute temperature is different from other temperature scales, such as Celsius or Fahrenheit, because it is a true measurement of the average kinetic energy of particles. Other temperature scales are based on arbitrary reference points, while absolute temperature is based on the fundamental properties of matter.

## What is the relationship between absolute temperature and average translational kinetic energy?

The relationship between absolute temperature and average translational kinetic energy is directly proportional. As absolute temperature increases, the average translational kinetic energy of particles in a substance also increases. This means that at higher temperatures, particles are moving faster on average.

## What are the units of absolute temperature?

The units of absolute temperature are typically kelvins (K). This is the standard unit used in the International System of Units (SI) for temperature.

## Can absolute temperature ever be negative?

No, absolute temperature cannot be negative. As mentioned earlier, absolute zero is the theoretical lowest possible temperature, and it is defined as 0 K. Therefore, absolute temperature can only be positive or 0.

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