# Intermolecular forces and temperature

1. Feb 27, 2015

When the temperature of a fixed volume of gas increases (higher average kinetic energy), the effect of intermolecular forces becomes less prominent. That's very intuitive, but how can I understand this in terms of force, velocity, momentum and so on?

2. Feb 27, 2015

### imawesomeYKI

well bruh first of all im a new guy and a very exploratory and curious student...lol
so it must be the weight decreases due to the expansion of gas or just spreading of molecules(force),it must be the density of air somehow effecting the speed thus stuff happening(velocity)....

so yeah thats what i think

3. Feb 28, 2015

### jfizzix

If the gas you're talking about can be thought of as a van der waals gas, then the reason the effect of intermolecular forces becomes less important at higher temperatures (and constant volume) is that the correction to the pressure due to the intermolecular forces is constant at constant volume.

As the temperature increases at constant volume, the pressure increases, while the correction to the pressure remains constant, becoming less and less significant as a result.

For a more satisfying mechanistic reason, the faster moving the gas is, the impulse (force acted over time) imparted to a particular atom of the gas in the time it would take to travel a unit of distance is smaller at higher temperatures because that atom travels a unit of distance over a shorter time.

Because the exchange of momentum with the walls of the container is what determines the pressure, we can see that at higher temperatures the effect of intermolecular forces on the gas becomes less and less significant.

All this is an approximation though. If you got the temperature high enough to turn the gas into a plasma, or so that nuclear forces need to be taken into consideration, I couldn't say.