What force accelerates a heated air molecule?

[mmanyevere]

Hi All,

I have always been made to understand that the reason why gas expands or causes pressure build up when heated in a sealed container is that gas molecules speed up when heated. If this is correct, can someone in the know please explain what is happening at the individual molecular level how absorbing heat energy can cause a molecule to change its speed.

Assume a single gas molecule in a 1 cubic meter container at temperature T1 moving at speed S1, if the temperature is increased to T2, does its speed increase to S2 resulting in more frequent collisions with the container walls? Exactly what mechanism is at play to cause the increase of speed and in what direction does the speed increase? If the speed does indeed increase, then there must be acceleration which implies a force. What kind of force is this? Why does this force always act in the direction in which the molecule is already moving?

Thanks for any help.

Marco.

 

[russ_watters]

You have to consider where the heat comes from. In a chemical reaction like burning, the heat energy comes from chemical energy of released/reformed chemical bonds. Think of chemical bond energy as a rubber-band (actually, its magnetic) - when the energy is released, the molecule formed/liberated is essentially flung away in a random direction, like a slingshot. A container full of, say, hydrogen and oxygen that are ignited ends up with just faster moving water molecules.

Now, that heat energy can then be transferred via blackbody radiation (the heat you feel by standing near an open flame) or conduction/convection. Conduction and convection work literally by having energetic molecules hitting less energetic ones and transferring their momentum, like balls on a billiards table.

 

[astrokreng]

Hello Marco,

Thank you for your question. The force that accelerates a heated air molecule is the kinetic energy of the molecule itself. When a gas molecule absorbs heat energy, it gains kinetic energy and begins to move faster. This increase in speed is what we refer to as an acceleration, as it is a change in velocity over time. This change in velocity is what causes the molecule to collide with the container walls more frequently and with more force, resulting in an increase in pressure.

At the molecular level, the absorption of heat energy causes the molecules to vibrate and move faster. This increase in movement and speed is due to the increased kinetic energy of the molecules. The direction of the speed increase depends on the direction of the molecule's movement before the heat energy is absorbed. This is because the heat energy is transferred to the molecule in the direction it is already moving, causing it to accelerate in that direction.

The force that is responsible for this acceleration is known as the intermolecular force. This force is a result of the interactions between the molecules and is responsible for the movement and collisions of the molecules. In the case of a heated gas molecule, the intermolecular force increases as the molecules move faster, resulting in more frequent and forceful collisions with the container walls.

I hope this explanation helps to clarify the mechanism behind the acceleration of heated air molecules. Let me know if you have any further questions.