# Container filled with gas - interaction between the molecules

1. Dec 30, 2011

### edyacc

Hello there,

I'm studying thermodynamics right now, and a question popped into my mind for which I haven't found a decent and detailed explanation so far. Say that we have a container filled with any kind of gas, and we can control the temperature of the wall of the container. If we increase the temperature of the wall soon the gas inside heats up as well. I'm curious how is that heat dissipated from the wall to the gas using a microscopic view (like: due to the increased temperature the molecules in the wall the start resonate more rapidly and the molecules of the gas collide with the molecules of the wall and blablabla...) If you can answer or tell me where can I find a comprehensive study concerning this, I would be very grateful!

2. Dec 31, 2011

### edyacc

A day passed and still no answers :(
Let me rephrase then:
Is there an explanation for how the transfer of energy/heat happens between solid (wall) and gas molecules on the atomic scale?
Pretty please, I'm really curious. Someone help me?

3. Dec 31, 2011

### Studiot

Hello edy, welcome to physics forums.

This is a very good question, but not the best time of year to ask it.

However here is a simple kinetic theory explanation.

Consider the particles or molecules. Any molecules, gas molecules, container molecules whatever.

A collision, capable of transferring energy (heat) is said to occur when the distance between the centres equals the sum of their radii.

The probability of a collision depends upon the size of the area defined by this sum and is often called the effective cross section and given the symbol sigma (σ).

The rate of collisions depends in turn on the probability and the rate of energy transfer upon the rate of collisions.

So ultimately the rate of energy transfer depends upon the effective cross section.

Now if the wall molecules are moving with increased vibrational speed and amplitude due to increased temperature, their effective cross section is increased, increasing the rate of transfer.

Another way to look at this is to to say that the increased cross section decreases the mean free path length between collisions.

go well

4. Dec 31, 2011

### klimatos

Energy (heat) travels from the wall to the gas in two ways: electromagnetic radiation and conduction (transfer of kinetic energy).

The walls and the gas both emit photons, but the wall being hotter emits more. The gas absorbs more photons than it emits and grows warmer.

The molecules in the wall also vibrate in place. This kinetic energy of vibration can be transferred to the impacting gas molecules as increased kinetic energy of translation. Imagine a golf ball hitting a strongly vibrating panel.

Quantum considerations keep the wall's kinetic energy of vibration from being transferred as increased kinetic energy of vibration for the gas molecules. The energy needed to get gas molecules to vibrate is much, much greater [about 5ev] than energy available from solid molecule vibrations.

This increased kinetic energy of translation of the gas molecules is measured as increased gas temperature.

For more detail, see books on kinetic gas theory, statistical mechanics/statistical thermodynamics, and quantum thermodynamics. Note that these are in increasing order of difficulty.